Yes, you can decline services of the appraiser the lender chooses - however there may be a fee involved (like a cancellation fee).
If this is the case and you let the appraiser know you are not going through with their appraisal (before they perform the appraisal), you’ll need to call the lender or your real estate agent and let them know the reason why you declined the appraiser so they can send someone else out to complete the appraisal.
However, if you decline services of an appraiser who has already come to your home, there may be a cancellation fee involved.