Can Mew ex's "Genome Hacking" attack copy an opponent's VSTAR attack that has already been used?

Yes, Genome Hacking can copy an opponent's VSTAR attack, even if the opponent has already used up their VSTAR attack for the game. However, if you have already used your own VSTAR Attack you cannot choose to use a VSTAR Power attack with Genome Hacking; you must select a valid attack to use.

Relevant cards

SV35_151