So uh, I had no help here and tried it anyway. Didn't go well... thanks....
Oh well. Now the real question is, how can I edit the volume code in Project M if I can't use Brawl Song Manager's volume adjuster? Fountain of Dreams is too loud, the N's Castle Medley I downloaded is too quiet...

So I downloaded Lakora's Song Manager and it is spectacular. I just have some questions with how it works with Project M. Specifically the Custom Song Volumecode which lets me add volume to a custom song (in case I want to put something over Pokefloats). But to my knowledge I have to save it over the GCT codeset. I don't know how this would work with Project M because (once again, I may be wrong) it has a different GCT codeset. Would it work, or do I have to do something else to make it louder?

I think I'm gonna wait for version 3.5 to mess around with the Stage Expansion Code, thanks for the help guys!

So what I do is, go to Lakora, put Base .REL as Final Destination and To Replace (w/e), then put the .rel in the folder, and put the STGCUSTOM1D.pac in the stages folder and rename it to match (w/e)? Got it. Now, I read the mentioning of a stage expansion code so naturally I googled it and found a dl link on Smashboards, and I have no idea what any of it means. (I'm new to like everything sry ) so http://prntscr.com/51srm0 I got all this and I don't know what to do with it nor do I know if I can use the stage expansion code for 36 stages without having 36 stages (like if I want to use the 36 stage code and only put like 20 stages).

I opened it in Brawl Box, it says STGPEACHCASTLE64, but it has a thing saying it can work over many stages like Final Destination or Green Hill. Does this mean I can just use it over any stage?

Well my Peach's Castle doesn't have a .rel, it just has STGCUSTOM1D.pac o.O

Another note, I downloaded Lakora's SSSEditor and I have no idea how to use it with Project M, I can't find a GCT in the pf folder. And I still dunno what to do with my Peach's Castle stage...

Well the thing says "Base .Rel" and "To Replace". I'm just getting really confused, it doesn't feel clear to me. Like this is what I downloaded http://prntscr.com/4z2o48 and I have no clue what to do with it. Also, I have no idea what a stage expansion code is, and even if I did, I wouldn't know if it works with Project M cuz that's what I mainly use (srsly, the gameplay is a lot better).

Ya, but I don't have a .rel file, I just have the pac file for STGCUSTOM. How do I add it to the game without replacing anything or how can I add it replacing something? This is where I'm confused.

Stage Expansion? ......What is that...? Also, I still don't get what lakora.us/rel has to do with it.... like I see STGCUSTOM in the "to replace" area but I don't have a .rel for STGCUSTOM just a pac.... am confused...

What if a stage doesn't have a .rel file? I found a Peach's Castle map and it only has a "STGCUSTOM1D.pac". What do I do then? What does Custom1d even mean?

I know I've been asking a lot of questions a bit lately, but that is a bit because I'm new.
A question I'm having is like, I see stage hacks for certain stages, but can I use any hack stage with any regular stage? I really don't like Rainbow Cruise as a stage... so if I download a map in the green hill zone section, can I just switch the name of the file to whatever Rainbow Cruise's file name is or does a map that replaces Rainbow Cruise HAVE TO BE in the Rainbow Cruise category?

I have a normal Project M (although I did hack a lot of characters into it) and not any sort of custom build. It just acts funny in Stage Select.

So I've been hacking Project M a lot, and I tried replacing Menu 1 with This Will Be The Day (just put the song into the folder and edited the info.pac and the mu_menumain.pac, like I do with my other songs). It worked fine until I got to the Stage Select, then the song played for a moment and then it stopped until I went back to my previous screen (CSS). And also sometimes when I either go back or select my stage, it like freezes for a sec and my controller vibrates and then goes back to normal. https://www.dropbox.com/s/jrqmhbtakrj8rbp/T03.brstm here's a link it is by A Bloody Canadian. I have no clue what the problem is. Did I mess up or is it just not possible?