There are two user_confirm()'s in all of my posted scripts. One of them is in the update checking function, and one of them in in the MacGuffin script because there is no way to know whether or not a wooden wheel has been used without possibly wasting turns or straight up asking the user. I don't think that is too many changes to make to your local code.
I know you don't want to add this, but I wish you would reconsider. Just as you think it is trivial for me, or someone else, to edit the files, I think it would be trivial to add a few lines to make it optional but default to use user_confirm(). The difference is, your trivial change shows up in everyone's code, every time they download it while changing it locally means everyone who wants it needs to make that change every time it was downloaded.
The other part is that zlib is a very useful library, and it is used by 6+ scripts already and no doubt going to be used by even more. And all of those scripts use check_version(). While zlib doesn't update frequently, I probably can't say the same for BBB, macguffin, Wossname, dailydungeon, or my own libraries. One of those is probably going to update every few weeks.
The third is I don't like local changes. It is bad enough I have local changes to KoLmafia (my crafting patch) which I can't take advantage of any useful script, it gets more cumbersome to work with minor changes to scripts. And, it is makes it even harder to remember to make a change when you update only every few months, and it won't become an issue until it nails you.
Yeah, I could make the change locally, but I really wish you would consider putting it in. I don't mind if you make it default to always use it, or require me to solve a quadratic equation to figure out what to put in there, but I'd like it to be part of the pristine zlib instead of local edits.
EDIT: I'd also like to see the macguffin question defautable with a setvar(). At this point, I only use macguffin for that question, so I already know the answer.