L Lily Scott healing takes time, and you've been really great about monitoring his incision! Taking pictures so you can compare his progress over time was a very smart move. I would continue to monitor it and leave it alone and let the healing do it's work, IMO it looks like he's healing up very well.What would you use it for? It is for abrasions, cuts, wounds, etc. I don't see any of that still going on, do you? Tbh, there doesn't seem to be anything going on that still needs healing 'sped up'.
I know you are worried about the protrusion, but that might just be scar tissue that occurred due to the many times the incision was re-opened and re-healed. And some cats are prone to developing scar tissue (just like humans) anyway.
Maybe just save it for a time when he gets a scrape or something that might need some help in the future?