I have white pimples 20 days after FUE -- can I pop them?

It is best to contact your doctor about post operative care and instructions since each doctor has a different regimen.  If you have an infection your doctor can help you with treatment options.

It is important that you treat these before they do get too bad. Folliculitis can kill the transplanted grafts. Follow up with the doctor that performed the procedure and get aftercare instructions. Antibiotics and some specific creams may be necessary. 

This is a classic case of folliculitis, with pustules that need to be drained and cultured. Appropriate antibiotics should be prescribed with recommendations to use warm wet soaks. by your surgeon

White pimples and redness are indicative of an infection. You should contact your surgeon to get effective advice and treatment. Scalp infections are generally treated with oral antibiotics.