could i renew my FI rating on a microlight and apply for a microlight FI with this license/med combination?without further hoops to jump through?
As your FI is also legally valid on a Microlight, then in theory you could do a FI Microlight test and apply for a separate FI Microlight qualification but, you cannot renew or revalidate the FI(A) rating using microlight instruction or a test on a microlight.
Whether or not the powers that be can get to grips with this combination is another matter.