Thanks for the clothing links, I will check the free ones. The CK_Boxers_01 do not seem to work however, the kind of do not attach correctly to the skin.
Regarding the "property to store or not" point: In VaM, the system to hide the penis on
males is determined by wearing pants (or underwear) with the
DisableAnatomy property set to "true". This is a property that is attached to each clothing item - typically "true" for pants, underwear etc, and "false" for shirts, hats, socks, etc. This makes sense, because the penis should only be hidden if clothing items are worn covering the genitals.
To my knowlege there is no other way to hide or unhide the penis on males but to go through all active clothing items and check whether there is one with DisableAnatomy = "true", and then et this to "false" if you want the penis to be shown. If any one item has DisableAnatomy = "true", the penis will be hidden (even if it's a hat

. BTW: The Mbriefs by maru01 you linked already have the DisableAnatomy property set to "false" by default to allow for the sim effects without hiding the penis.
Or are you talking about alt futa?
On
alt futa, the DisableAnatomy property unfortunately does not work, probably because the entire genital is added by Stopper's plugin. I therefore use the Adjust Glutes property (also attached to each clothing item) and Stopper's "hide material" property to automatically hide the penis when an alt futa is wearing underwear/pants with the Adjust Glutes property = "true". The ugly side effect is that larger parts around the penis are hidden too and leave a black hole which can be seen often with smaller underwear. I also think there is no way to make an unhidden penis work for clothing items like AWWalkers boxers you mentioned - no matter how flaccid or small the penis is, it will not be covered by the clothing item.
Or do you mean you want the fold/unfold system be separated from the hiding mechanism (on alt futa)?
After all of the above, I obviously still don't get exactly what effect you would like to achieve. So please, help me!