The change fee is assessed or waived at the time of the change. So your status when you make the change is what is important.

If you need to change a flight and aren't MVPG yet, you can cancel it and just retain the ticket number, and then cancel for credit or change it once you attain MVPG. Then you can deposit in your wallet or reuse the value without a fee.

Conversely, if you are MVPG, make any necessary chances/wallet deposits before you lose status.