The departments HR office has the ability to make a change to what is known as the "Reports To" supervisor in the HIP system.  When changes need to be made, HR can do that.  The employee or their supervisor cannot modify the Reports To supervisor information in HIP by themselves.  When a supervisor position is vacant, HIP will route the employee's request up to the next available supervisor in the department hierarchy.  Usually, TA supervisors are not used by HR to be the Reports To, but in some cases, HR can make the TA supervisor the Reports To if the department requires that.