The tyranny of the HOA. Your options for what to do with your property is very limited

Not exactly, because n commits will have been squashed into one, so making the edit would lose the reference to the originals which should have been squashed with other commits

See but you can break the commit back apart by doing a git rebase interactive, selecting that squashed commit as the commit to edit, then doing a git reset HEAD~1 then recommit it in pieces, then git rebase --continue

Then git rebase -i a second time and then remove the commit that you don’t want to be included

If you are continually rebasing and having to fix the same merge conflict over and over, you should look at https://git-scm.com/book/en/v2/Git-Tools-Rerere

You can also do a git rebase -i and mark a commit as edit and git will stop at that commit in the rebase to allow you to stop, look around, and make changes… I think that is what you are looking for