Im currently learning houdini, mostly flip and bullet. (Coming from XSI)
Doing some rnd on a Beer simulation with the Flip solver.

Im using POP VOP to switch between beer and foam based on acceleration.

I got two questions.

How do i make a “One way switch” (the foam will never switch back to beer liquid) ?

Is it possible to make a attribute that will operate on a per frame/substep level. ex: making a custom life attribute that will start subtracting a value from the foam particles when the velocity is less than X ?