The main issue is whether or not there is a potential for contamination of the implant during the surgery. If there is even the slightest risk of contamination I would advise waiting until the catheter is removed.
Yes it is technically possible but your PS may advise against it. The risk of infection may be higher as you have a portacath. The potential of 'seeding' of the new breast implant may be a problem. I would wait for the portacath to come out. Hope this helps