I couldn't find a tutorial on how to do this anywhere, so I figured it out just now. I wrote a tutorial for myself, so I'll post it here just in case there's anyone in the same situation I was in! It might be obvious, but I managed not to find this out until today, so . . .So, you've made a beautiful texture, exported all the files, linked them together correctly, and made a wonderful mesh. You import into Bodyshop, only to find - The alpha/texture is wrong!
Noo!!Don't worry, a few easy steps will sort you out. Well, it's a
bit more complicated now, but it's not too complicated. If a ditz like me can do it, you can too!
- Edit the texture or alpha in your graphics editing program until it is to your liking. Save over the .bmp but don't press import in Bodyshop (you can press update texture if you want to see the texture, but don't import).
- Close Bodyshop - you won't need to make a new recolour package!
- Copy the recolour package for this project from your EA Games\The Sims 2\SavedSims folder into your Documents (or wherever else you're keeping the mesh files you edited).
- Duplicate this recolour package so you've got a backup if it all goes horribly wrong. Put it somewhere safe.
EDIT: Tenshii let me know about the Import function reducing image quality. Be sure to download and install Legacy DDS Utilities, to enable an option called Build DXT in SimPe when importing your new texture later, to avoid all that horrible blocky badness!!
To enable Build DXT after you've installed the DDS Utilities, go to the Extra>Preferences menu in SimPe, and where it says Nvidia DDS Tool Folder click Browse and locate where you've installed it to :-)- Open your recolour package in SimPe. On the left list click on Texture Image (TXTR) and then to the right of this find the texture which is incorrect.
- Enter plugin view and you'll see that texture appear at the bottom when you click on it. SimPe combines the texture and alpha so you'll see parts that are see-through, if the alpha file tells them to be.
To change the texture (Not the alpha):- Right click on the texture that pops up and a drop down menu will appear. To update the texture, click
Build DXT . . . and the DDS Builder window will pop up.
- Click on the left where it says
open Image . . . and locate the texture you've edited. Press OK and a preview of your texture will appear in the left box.
- There's a drop down box on the right called
Sharpen. We don't want this to do anything so click on the drop-down box and select
None.
- Press the
Build button and wait for it to finish its business.
-
If everything's to your satisfaction, press
Commit and
Save, and you're done!
- If the new image is showing coloured parts where it's meant to be see-through, or if you want to update the alpha anyway, read on . . .To update the alpha channel:- Right click on the image in SimPe to bring up the drop down menu. Instead of
Build DXT . . . choose
Import Alpha Channel . . .- Change the file type to .bmp and select the alpha channel file you've edited. Press Open.
- Wait a moment while it sorts itself out and your texture will be newly updated with the alpha channel in place (see-through parts will be see-through and not coloured in).
- Press
Commit. This takes a moment, so don't go clicking everywhere while it's doing it. Don't save yet, or it will be all pixelated.
This bit, I've nicked from Tenshii~Akari's Infant Diaper Override Tutorial. I'll put it in my own words:- Right click on the texture in the
TXTR Editor and press
Export . . . Don't change the file name of this export, just save it as it is. I had problems when I changed the file name, so don't do it.
- After you've exported it, right click on the texture and choose
Build DXT . . . again. Do the same as when you built a DXT before, but this time import your .png file. If you've got 'view icons' on in Windows, you will know you've done it right because you'll see the preview in the Open window is your texture surrounded by white (this is the see-through bit). Wait for it to finish its doings with the DOS window.
- Finally,
Commit, and
Save!
- Copy your newly saved recolour file from your project file into the EA Games\The Sims 2\SavedSims folder, rewriting the old one (you've already got a backup of this old one just in case, haven't you??)
- Open up Bodyshop, and your texture has been replaced. Hooray!!

This was bugging me for years lol.
*Ang*