no, because Ness's bat and Link's sword are both part of their models. the reason you can take Ike's sword is because that's one of his articles (Ike also has a sword attached to his model, but has his sword as an article for his Up B attack).
of course. basically the reason that the throwing and being grabbed glitch occurs is from having an incorrectly placed HipN bone, or just not having one at all. once the HipN bone of the new model matches the HipN reference that the original character had, then it won't freeze when being grabbed.
so ZSS over Marth, huh? let's see ... wait a minute, they already have the same index for the HipN bones... are you sure whoever did it for you did it right? all of Marth's and ZSS's important bones (TransN, XRotN, YRotN, and HipN) already line up without the need of any editing. check the ZSS model real quick, and see if the 12th bone (index 11) is the HipN. if not, then that's the problem. otherwise, he might have changed a reference he shouldn't have. if you know how to use Tabuu, then check the HipN bone reference to see if it's 11 like it should be. or if you want, you can send me the model and i'll check it.
and the way the trophies are, they're stuck in they're pose. the bones are absolutely no good to do anything with, other than rotating and resizing the whole thing. but assist trophies, they work, but as with most replacements, they will need some work done to them.
well, yes they would. but with some characters, the stretching is hardly noticeable. but if you took a smaller character, say Olimar, and put him over a large character, say DK, then yes, the stretching would be pretty noticeable. so it really depends on the characters you're swapping.
but it wouldn't matter if you made new animations (or edit the current ones to fit) for the new model. of course though, that would just take too much time to worry about.
balanced? about as much as Ganondorf is regularly, i guess. i've never been too up to date on what counts as balanced, but there's no major cheap moves. for the most part, it's basically just Ganondorf with DK's model.
and Overlord, yes, it's fixed for Ganondorf. it works just fine, no glitches or hurtbox errors. i took care of that myself.
basically, you only need to add bones if the new model has less bones than the replaced character's model, as in if you have a model that has 40 bones, and you want to put it over Mario, Mario has 62 bones, so you would need to add 22 bones in order for it to work. if the new model has 86 bones and you still want to replace Mario, then there's no need to add bones.
resizing is a little different, but really only applies if the model is from a game other than Brawl, and even then it depends on the game. models from Pokepark Wii need to be scaled up about 2 or 3 times what they are, but Animal Crossing models need to be scaled down to about 25% of what they are.
a one slot swap is just putting one model over another character, but making it work with the replaced character instead of editing everything to fit the new model. here's a few examples, and they should be in the Vault. one is Geno over Lucas, Geno being a vertex edit of Toon Link. another is Imp Midna over Sheik, Imp Midna being another vertex edit of Toon Link. another is Phoenix Wright over Sheik, Phoenix Wright being a vertex edit of Little Mac. they all act and fight as the character they're over and not as the character they were originally, and that's what makes them a one slot swap.
as for how you go about doing these, i have a basic guide of what to do.
the PSA file (the FitCharacter.pac), there's no current way for it to only apply to 1 texture.
the MotionEtc.pac though, it can apply to only 1, but it requires renaming 1 or more bones, then re-animating the new bone in every animation (all 300 of them). so this one is possible, but it takes a bit of work to do. and this is how one slot size mods work, is just by renaming a bone, then scaling it to fit.
section 3 tells you about that. but if you already know where the costume files go, the movesets and animations just go in there as well. so if you have a FitMario00.pac/.pcs file, and you want new animations with it, just put the FitMarioMotionEtc.pac (and the FitMario.pac as well, if there is one) in the same folder as the FitMario00.pac/.pcs files.
for 1) to put it simply, a character import is a character that has a different character model on top of them. they don't necessarily need a logo, CSP's, or moveset, but it does certainly help.
for 2) most of them don't need extra codes, unless they're over the Alloys or other characters you can't normally choose to begin with. all you absolutely need is the FitCharacter00.pcs for the new character to show up. and as Zigheart said, many times because of different bone names, they need custom animations in order for them to be able to move, otherwise they'll just be stuck in their t-pose. but if it's a character that other's have been working on, then usually there's already a good amount of animations done, and sometimes a file that alters how the attacks work in order to match up with the new animations. the files for those are called FitCharacterMotionEtc.pac (for the new animations) and FitCharacter.pac (for the altered attacks, usually called a PSA file). so for a more complete character import, it will have the costume files (FitCharacter0X.pac/.pcs), new animations (FitCharacterMotionEtc.pac), and a PSA file (FitCharacter.pac). most characters in the Vault should have all of these files, but it depends on the creator. full character import projects take a long time to do, especially if you have to make all new animations (there's about 300 animations per character). and no, you don't have to do anything yourself, unless you want to make a character.
well, lets see if some pictures help. there's really only 2 main steps, finding the offset, and changing the reference.
to find the offset, open the FitCharacter.pac (the PSA file) of the character you're replacing with Tabuu (the program). i'll use Ganondorf as an example, since i just edited one for someone. open the FitGanon.pac with Tabuu, and go here.
the Value is what we're looking for, because that's the HaveN index that the items link to. now, convert that value to hex using the Windows Calculator (or some sort of Decimal to Hex converter). converting 65 to hex gives me 41. do the same for the 0x001 Value, which is 56 for Ganondorf, 38 converted to hex.
now that you have them converted to hex, open the FitCharacter.pac in a hex editor, then use the search function to find the proper reference. when i open the FitGanon.pac in the hex editor, i search 00000041 00000041, because it will take me right to where i want to be, which is here.
i highlighted the section that has the references you need to change. there's 9 spots that need changing, 3 HaveN references, 5 HandN references, and 1 ThrowN reference. the other picture i posted also shows which ones to change from here. the 00000041 bits are the HaveN references, the 00000038 bits are the HandN references, and the 00000045 is the ThrowN reference. change them to match the new model, and don't forget to convert the bone index numbers to hex before entering them.
after you change them to what you want, it should look something like this.
the parts that are red are the new model's references. for this, it's actually a DK model. the 00000036 is DK's RHaveN reference (bone index 54), the 0000002D is DK's RHandN reference (bone index 45), and the 0000003E is DK's ThrowN reference (bone index 62). once changed, save it, and you're good to go.