You can use a memory variable for your aspect name as well (just like your target). Just make sure it is a string.
So on the memory tab of the AI (second tab) add a variable, make it a string, put in the name of the aspect you want (no quotes here, RAIN already knows it’s a string since you selected it). In your behavior tree, use the variable you made instead of putting in the quoted string (again no quotes, as it is a variable in this case, it just happens to contain a string).
Does that make sense?
You can change the aspect you are using at any time by accessing the variable you made in WorkingMemory. It’s a string instead of an aspect though, and you can read or set it to whatever you need at the time:
AIRig rig = GetComponentInChildren<AIRig>();