modifying built-in TGAs - do others see them?

I've used the TGAs in the "character" folder to preview textures. My avatar doesn't always "bake" the textures; often I have to go into the appearance editing mode to see them. But sometimes they do. But does anybody else see the modified textures if they're in my viewer (does the viewer upload the textures to the grid)? I'm using the current OS X viewer and haven't found a menu item to force textures to "bake." I suspect that isn't, paradoxically, LL's fault Anyway, thanks in advance for any help or insights!

If I'm reading you right, what you're doing is testing clothing on your avatar by temporarily replacing the TGA's in you character folder, and then going into appearance mode to see them. If that is indeed what you're doing, then the answer to your question is no, at least to a point.

As far as I know, no one will see the altered textures but you until you exit appearance mode. So, as long as you change the files back to normal before you do that, nobody will ever see what you're working on.

Thanks! So, can I place my "permanent" skin in the character folder instead of uploading and wearing it, and still have it visible to others? it seems like that might be a little more efficient WRT textures. But it also seems like using another viewer (not that I ever, ever log in from work would overwrite the custom stuff I put in the character folder.

I used to have a skin from Second Skin that did exactly that, it was downloaded and inserted into the character folder, and you are also correct that if you log in somewhere else, it will not be seen, and I do beleive it will be overwritten with an update.

Yeah, just as Dnel said, modifying anything local on your machine will affect just what's sourced from that machine. So, when you log in on another machine, you'll be using the default stuff unless you also modify the same files there. And yes, the changes will be overwritten every time SL is updated.