I have carved away wire marks on F. Benjamina when they were probably under 4 yrs old. Now 10-15 yrs later, you would never know.
BUT what I did and what you are wondering about are pretty different. The species seems to be quite tough as far as care and feeding go. However that borders on big enough to girdle the tree if you cut it flush. It may send out roots. Thought of air layering it? Branches in the vicinity of a layer cut add to the likelihood that it will push roots.