I don't think this is possible with the built-in functionality.  But you could consider adding your own reassign functionality.  You could turn off the ability to reassign the form to disable the built-in option, and then put your own version inside the form itself, using a drop-down of valid options.  Rename one of the form buttons (Approve, Reject, or Submit) to something like "Reassign Form".  Set the outgoing path of your form when the user selected that option direct to a task that assigns the form to the "team based on a variable" and use the value of the dropdown to select the appropriate team.

Its a workaround for sure, but it should work.