I'm doing multiple animation on a humanoid who has some kind of a sword carrier (I don't knonw the exact word). And so this sword carrier AND the sword are both parented to a leg bone , but only for the walk and run animation. So I'd like to know if there is a way to clear the parent of the leg bone and parent it to the hand bone but only for the attack animation. Hope you understood what I'm searching for and that you can answer me :D
The only solution is the Child_Of constraint if you want to alter parenting in pose mode. If that leads to another problem, ask it, there is probably solution to it.
Make sure the bone that is gonna get the Child_Of constraint has no parents. Else you will get multiple parent transformations (the original parent and the constraint on top).
There is a way to rig an inverse parent transformation to negate the original parent (if present) when needed from pose mode, but it is complicated and probably not worth it.