yep, don't be afraid of assigning UID's, it's actually quite simple once you've done it a few times.
First you'll need to give enemy01_box an instance variable which will contain the UID of the actual character sprite. I'll call the variable "CharUID"
underneath "pin to..", add another action:
-> enemy01_box set value CharUID to enemy_01.UID
and then after this, in order to pick the correct character sprite for the box, add the following underneath the "For each.. " condition:
+ enemy_01 pick instance with UID: enemy01_box.CharUID
*edit: I accidentally typed "enemy_01.uid pick" instead of "enemy_01 pick"