FOSS gamedev and creative worlds

Hello,
I've been working on a ww2-based map for pvp and was wondering if it would be possible to create a mod that allowed a player to change stances (standing to crouching to crawling). This would open up huge realms in not just my map but many other peoples' as well.
Thanks for the insight!

AdventureTest by BrandonReese has support for sitting and lying down. There are no further animations in the player model (apart from walking, mining and walking and mining simultaneously). He also posted an instruction of how to use sitting/lying for players.

Excellent! Could you point me towards that instruction?

Nevermind, I found it. Thanks again!