I have been creating clothes and things for the Sims 3 for a while, but I have wanted to try making some default replacements. There are many CAS tutorials for clothing, showing you how to make new clothes, but nowhere are there instructions on how to make the things you make into default replacements. I think there are eyes and things that are default replacements. So if someone has made those, I have two questions. Is it possible to make default replacement clothing, and if so how?

I know it used to be the only way to make new things was to replace the old, but I wouldn't know how to do it. >>
You could try poking through older tutorials, perhaps?

Yes, it's entirely possible. Really, all you need to do is replace whatever resources from the game itself with the same type of resources (DDS images, for example) that have the same Type/Group/Instance (TGI) of the originals, to make a default replacement. For clothing, the original TGI can be found when you do a project for it in CTU, and then after you save your project you can open it in S3PE and change the TGI back to the original to make it a default.

Which of the TGI numbers? There are many according to CTU.

You can make a default replacement clothing item or accessory by packaging your new mesh with CTU and NOT renaming TS3's default name of the item before saving. I know this because I once inadvertently made a default replacement for something when I didn't mean to, and discovered that the item had to be renamed in order for it not to replace the default one!

The TGI that HP is referring to is probably TGI0, the bump map, which is the only texture you can't replace from within CTU. You can either replace as she says above, using s3pe, or by changing TGI0 in the Group comments in Milkshape to the key number of a neutral bumpmap, which is what I've done.