I have a travel request workflow that was built in such a way that when I need to change the list it stores values in (because the workflow errors after 5000 records are stored) then I have to go into A LOT of activities to change them all to the SAME variable that uses the SAME formula to set the list. 

The activity is Set Workflow Variable, they had it set up the variable "strAssignedTo" to these values:

     - Equals: List Lookup
     - Source: The new Workflow Tasks list you just created
     - Field: Assigned To (click on the X to change it to Login Name)
     - When: GUID
     - Equals: Workflow Variables : strTaskItemID

Can I set the "Source" on this formula to a variable that I can change just once at the top of the branch and not have to do this 50 times every time? I am unable to choose any variables in the drop down.. Is there a way to build this even if it's complicated so that I still only have one thing to change?