Ok... hmm well theres a couple different things it could be.  You have to save it as the correct name, and in the right place.  Make sure that if you go back to pf\menu2\ that sc_selcharacter.pac is still there, and with the same name. 

Also, if you replace a file with something that isn't compatible, it might cause it to freeze.  Like make sure you are putting the Etna CSP over the CSP instead of accidentally putting the Etna BP over the CSP...  The CSP needs to have dimensions of 128 x 160 pixels and has to be in .PNG format.

...A problem that could be occuring, but im 99% sure isn't, is if the sc_selcharacter.pac file is too large, the game could freeze upon trying to load it.  (I had this problem with the sc_selmap.pac)  The reason I dont think this is your problem is because I've added dozens of CSPs with no such problem.  However, feel free to look up the sc_selcharacter.pac file size limit on google or something and check to see if you're not over.

Worst comes to worst, go to the picture you replaced and replace it again with the actual picture it should be (found online somewhere)

Let me know

Alright so you'll need to use brawlbox.  There might be other ways to do it, but this one is pretty easy.
Anyway open brawlbox and then hit  file-> open-> and then go to your SD card (or wherever you keep your brawl files) and go to private\wii\app\RSBE\pf\menu2\and open the .pac file called "sc_selcharacter.pac"

Now you'll see a bunch of folders.  Expand the one called "Char_Bust_Tex_Iz77" and it will open to show a bunch of new folders named "MiscData(1 through 43)"
Expand a folder and then expand the "texture" folder inside that and you can preview the CSPs it contains.  Find the exact one you want to replace (Im not sure who Etna is, but if its Zelda by any chance, she's MiscData13) by trial and error and then right click on the picture you want to change, click 'replace' and pick the picture you want to substatute in.

Viola

Oh shoot! Im at 1.18.  Wow Thanks guys I would never have figured that out on my own. 

Any suggestions on how to lower this number? Like- does a certain image file type much smaller or something? thanks again.

Hey- need some serious help here.
I just booted up brawl through my SD card and homebrew (which Ive done countless times) but this time, after selecting characters and pressing 'start' the wii froze.  I've encountered freezing before, but ive always been able to figure it out.  It's not a specific stage thats freezing, but rather I can't even get to the stage select screen.

The last thing I did before this error was modify a bunch of stage-select-pics in brawlbox.  These were in the sc.selmap.pac file on my SD card (pf\menu2\sc.selmap.pac)  Once again, Ive swapped out SSP before and there's never been a problem.  I dont know what I might have done in order for this .pac file to cease working (which Im pretty sure is the root of the problem, since that pac file controls the stage select screen) but I've tried a bunch of things to fix it.

All the images i used as replacements were .png files like always, and all of them were the right dimentions.  Does any one know what might be wrong?? Thanksss

Hey soo.. first post anyone?

Anyway I was wondering if anyone could enlighten me on how I can make a 2D stage? I've made custom textures for characters before (w/ brawlbox and photoshop) but I've never done any vertex hacking...

Like how to take an image (or part of an image) and make it a playable surface in brawl?  Any help much appreciated

Thankss!