Interesting idea. Quick question: How exactly would it "genderbend" your character? Just set the pronouns/gender to the opposite? You can do that in the appearance menu with the preferred gender button. Would it invert the femininity/masculinity scale? That wouldn't actually impact various characteristics, leaving genitals, breasts, hips, hair length, etc. untouched, since that is only really about your character's facial structure and maybe the frame of the shoulders. Would it swap genitals? If so, what happens to hermaphrodites? Would they become sexless? Would it impact breasts? I can get female to male setting the breasts to flat, but what about male to female? How long would the dick be, how large would the balls be, if your characters race is a mix of several what race would the dick be? What happens if you use a gender-impacting transformative while wearing the equipable?
The point is. It is an interesting idea. But it also seems like the questions of how it would work mean that it either already has its function fulfilled (the gender can be set through the appearance, and masculinity/femininity alone are only really used for determining Steele's gender if it's set to auto), or it would be impacting a wider set of features which would lead to potential issues due to the complexity (if it transformed any features aside from plain masculinity/femininity).
Invert masculinity/feminity score, of course. While wearing the item, the user is immune to masculinity/feminity changes. In general, the item wouldn't work on sexless or herms.
I think primary sex characteristics like genitalia need changing, but also secondary sex characteristics like breasts and hips. The struggle, I think, is determining how to change numerical values of these characteristics across forms. I think that might need benefit from choice. Some transformatives allow you to choose a particular package of change. Here, you get the prompt for genderbending, and the player has the chance to choose the size of the penis, pussy, breasts, hips, butt of their genderbent form OR randomize these sizes. This prompt appears each time the user wears the item.
If the user loses their genderbent genitalia as a result of a tranformative, then the item reapplies the genitalia after a couple minutes in the form of that Codex timestamp update. This enables the user to experience scenes that might include growing or losing genitalia without conflicting with the genderbending item. Actually, after scenes, the item is programmed to check if the genitalia matches the masculinity/feminity score -- which is constant in the genderbent form since its immune to change. If the genitalia doesn't match, then the item prompts the user to choose again.
Not sure about hair, but that's not important anyway. I guess if you wanted short or longer hair, or a particular style after genderbending, then you can head to Tavros and get it cut, lengthened, or styled. Otherwise, hair carries over as is from form to form.
Basically, the narrative explanation is genderbending. But the programming doesn't need to reflect this. I imagine from a programming perspective, it's more like administering a transformative that retains its effects as long as the user wears the item.