Switching over the appraisal is simple, just ask for it and have it assigned.
The biggest hassle will be getting the old loan officer or mortgage company to release it. The appraisal belongs to the client, assuming they paid for it.
In an effort to extract revenge on the borrower / new lender, less than professional L.O.s will try to stall.
When asked, I've always surrendered the appraisal in a timely manner.... you never know when they will be back.
Yes RE/MAX, could you tell us a bit more about the situation? People often times have to go with an additional appraisal within a real estate transaction, so there must be more to the story...