I would consider 15004-15005 for the excision of the overgrowth/infected tissue and 15120-15121 vs. 15220-15221 for the skin graft for procedure you describe. The 15004-15005 is for "surgical preparation" for a skin graft and can include removal of devitalized tissue including scarring, necrosis, infection, etc. to prep the area for the skin graft. The final code(s) will be based on the total square centimeters of area prepped (this should be less than 100 sq cm if it's just immediately around the implant). The code(s) for the skin graft will depend on whether the graft is full thickness or partial/split thickness and the total sq cm.
I hope that helps!
Kim
www.codingmastery.com