First thing I want to say is that it’s ok for your close friend to think that. And it’s ok for you to want to treat him regardless. Treating relatively complicated or chronic issues in our pets isn't for everyone. It’s not perhaps for your close friend. But what matters is that you are making decisions that feel right to you. Decisions that honour the bond you have with this cat. So there will be people who don’t agree with you, but at the end of the day, they don’t have to honour that bond, that relationship. So it’s an easy thing for them to say, because they are on the outside looking in. So they won’t understand - nor can we expect them too. So it’s ok that they have this opinion.
I have this little dog who comes to see me, and I'm treating him for a variety of illness. Illness that some people just would never treat and euthanize him for. He’s 15. He tries to bite me. He tries to bite my staff. He tries to bite (and has successfully bitten) his owner several times. He also has one of the most magnificent bonds between a pet and person that I've seen. She calls him “a little shit” in the most endearing of ways. He’s a fantastic little guy. You watch your fingers, hug him and respect him. I love watching him prance - he has the proudest walk. I will be sad the day comes that he is not with us. He can bite me any time.
There is a saying - as a vet, if you never got bit once, you’re not working hard enough. So you’ve joined the club. Maybe his bite was a one off event. It’s possible. Some cat’s, as they feel better, begin to bite. Blocked cat’s always do this. And they feel good, they get feisty. Notice this is the absolute opposite interpretation of events that your friend has. There are some cat’s who will interpret something (petting for example) as pleasurable, but quickly decide they have had enough and will swat or bite because we failed to read their intentions. But sometimes they do want you to modify some part of their treatment regimen.
Often, they need counter-conditioning to a treatment or medications. Counterwhat??? This is a hugely under utilized technique when it comes to giving cat’s treatments. Because it’s currently explained in very technical or in-depth ways, mostly geared for veterinarians and technicians, currently, cat owners have no clear way of how to implement it for their individual situations. I will be trying to change that over the next 4 months. I am currently filming a video with a working title of “how to give them medications or treatments when they don’t want it” that will show these sort of techniques. As you have stated, you can test all aspects of his treatment (different needles, technique of fluids, add in anti-nausea, remove anxiety etc) to see if he feels better, perhaps resulting in less biting.
Good luck with your surgery!