Appraisal on duplex where 1 side is updated

[Josh V.]

The plan would be to keep the rented side as is until the tenant decides to move (assumed to be years from now).  Rehab current vacant side, rent it and refinance.  The question mark being would an appraiser give 50% at 'as-is' value and 50% at comp rates?  Is this common where sides are not equal? e.g. would I be rolling to dice on the appraisal?