https://pleyita.tumblr.com/post/186244319845/hi-jack-hope-youre-having-an-excellent-friday

Hi! I’ve actually struggled to do this for quite a bit because I didn’t understand how the frame/gender tags etc worked, I’ve only just started to get the hang of it so I don’t have a ton of great advice but I’ll tell you what I generally have been doing and maybe that’ll help!

• So basically, what I do is I first make the Feminine frame version of the clothing, and I untick ‘Restrict Opposite Frame’ and ‘Restrict Opposite Gender’ in Sims4Studio before I save it.
• Then I go in-game in CAS and try and test out whether it works for Masculine frames or not. Because I’m still very trial and error in my experience in this. If it turns out to make body parts go missing/looks wonky, then I know I have to use a separate mesh for the Masculine frame. If it looks fine then I don’t bother. For example, my strappy halter top looked fine on Masculine frames without any changes but my Masculine underwear needed to be done separately from Feminine underwear.
• If it turns out they can’t use the same mesh, I then have to find a Masculine frame piece of clothing that approximately resembles the piece of clothing I made on the Feminine frame. There’s not always a perfect equivalent, so I’ll have to improvise because I don’t know how to mesh so I can’t convert the Feminine frame one to a Masculine frame, I’d have to sit down and learn how to mesh for that! So I just find one that somewhat looks the same. (For example, I’m about to release some yoga pants that I made on a Feminine frame mesh that didn’t have a Masculine frame equivalent so they’re using different meshes but look almost the same. The Feminine version isn’t quite skin-tight at the bottom but the Masculine one is. It’s the best I could do in that particular case without meshing things).
• Then, I take the texture from the Feminine frame version, put it on top of the Masculine mesh, and inspect it to see where I need to re-paint it and adjust things. For instance, when I made underwear I needed to widen the front for Masculine frames as well as close the texture gap in the crotch due to the frame size difference.

• Once they’re done I tick the ‘Restrict Opposite Frame’ tag on both the Feminine frame package and Masculine frame package so they each only show up on their respective frame type. But they’re made to look similar enough that it resembles being unisex! You can then either merge the two packages, or leave them separate (I leave them separate, but it’s entirely your choice).

I hope this helps you out! I’m still a novice at doing clothes so I don’t always do it right and I have to do a lot of troubleshooting. But I basically require a lot of my clothing to be available on all frames due to my personal preferences, so this is something I’ve been trying to do for a while and I hope this can assist you in your own endeavor.