Strange as it might be to say it, there are some gaps in customization that I think could use filling.
First off, there should be something that lets you reshape vaginas like the Dong Designer does for penises. Presently, the only way to change vagina type is through racial transformatives, which can be unreliable to say the least.
Speaking of the D.D., how hard would it be to add a "template" function, maybe locked behind the Upgrade? Like, just copy the exact shape, size and color of one penis of your choice, and be able to apply it to another penis. (Seriously, I have no idea how difficult that would be or what it would entail coding-wise, but it sounds simple in my head)
Also, I think the recoloring items (Rainbow Gaze, Pickmentation and Pleasure Palette) should have separate categories for "Glowing" and "Luminous" (right now "Luminous" colors are almost entirely crowded out, only accessible through racial TFs) and maybe one for "Other," like "Hot White" and the Foxfire/Frostfire colors. It would also make it easier to add new "special" colors (Vantablack, RGB, stuff like that)
And finally, some sort of TF-Lock to prevent transformations to a given bodypart. Maybe have it be a software upgrade to Steele's medical nanites that you have to go to that guy in Uveto and jump through some hoops to get, and afterwards you can tell the bots things like "don't change my legs", "don't change my head" or "don't change my skin". Some things like parasite tails or the Treatment would be able to override it, but most one-shot TF items would be blocked from changing the designated areas.