I want to create a trigger action to clone a piece and then change which piece is selected from the initial piece to the cloned piece. Any thoughts on how to do this?
Select/de-select is not currently accessible from the module editor; so you would have to do something in custom java (so I understand from previous threads).
De-select trait is mentioned in the roadmap for V3.5.
I believe this feature has already been coded and will be released with VASSAL 3.5.0. So, you just need to wait a bit longer (a month or so, I would guess).