Be able to retrieve a Variable card #562
Description
To help reinforce the idea of the mutability of variables, it may be useful to allow the player to swap a variable card rather than replace it.
Describe the solution you'd like
A player played a V5 on an I1 in the past but now has a G6 with an Rx on it. They could replace the V5 with a V2 from their hand, and then on their next turn put the V5 on the Rx, as it is more useful there (going from 5 points to 30 points).
Additional context
This may add a lot of complexity to the game - both in gameplay and especially in coding. If there is only one V-card in a stack, doing a swap may not be too hard, but if there are two V-cards, we'd have to have a way for them to choose the V-card they want to swap.