...in SimPE alone? The only modification I want to make to it is to get it to use 512x512 images instead of 256x256, for higher image quality, and I'm willing to have my alteration replace the original (I only use my own recolors of it anyway, and if I am able to make the edit I will obviously be redoing them all).

(I would have to ask for the original creator's permission to share any alteration more involved than a recolor, though if I can easily produce a standalone mesh instead of a replacement then I will do so.)

Yep, you can. You can do it in Body Shop too, which is usually a better option as you get more compression on the images for smaller image sizes. Just make sure to change the texture, alpha, and bump map all at once.

Changing the image resolution is actually a bad idea for some inexplicable reason. I once changed a floodfill texture to a 1x1 image, figuring that a floodfilled image didn't need high resolution, so this would save space. The result being that it created this odd transparent "tube" effect on the sim. In short, not recommended.

Also, don't use Bodyshop. Bodyshop mangles the crap out of your images. I tested this once by importing a texture through bodyshop, and discovered it had turned into an inexplicably blurry mass of poo. Reextracting it out as BMP again to compare to the original, I found that the bodyshopped image had been badly damaged. If you want to retain your image quality as noncrap, import it directly as RAW32.

1x1 may not work, but other sizes definitely do. Maybe not universally - skintones and such, for instance, but accessories and clothing items such as toddler clothes that you may need to bump up from 512x512 to 1024x1024 works fine.

Body Shop doesn't universally mangle the crap out of images. It does compress images, yes, but the mangledness usually happens on dark textures - and you can often fix that by applying a very small amount of monochromatic noise to any areas that get that patchy effect. Can't see it in the finished product but it works fine for stuff like skin and clothes that can often get that weird patchyness where you meant to have a smooth gradient.

Huh, I could have sworn I had tried to do that in BodyShop before and failed. *tests* ...go figure, it works fine. Now I get to redo two sets of oddeyes plus a few assorted extras -- but at least they'll be prettier, AND it's a shareable edit. Thank you!

(Pes, I use SimPE from time to time for Sim content when I just can't deal with BodyShop's compression on a particular image, but I don't have the patience to circumvent BodyShop ALL the time. Besides, I get much better results now that I've learned to save all my progress in PSD even if I don't expect to need the layers later.)