I thought they either respawned (every 36 or so hours) or they don't respawn at all - It's a flag that you can set on each Container Base Object. If you can vary it, I don't know how (but maybe someone else does

)
Yes it will replenish whatever is missing (but if it uses levelled lists, then not always replace with the same thing as the PC levels up, you'd need to look at the list itself for that ... or use static items instead of lists)