Welcome to the club. This thread: The new Guild UI and Permissions...yikes (Part 1) was started nearly seven years ago when the issue in question popped up. It has been continued in this thread: The new Guild UI and Permissions...yikes (Part 2)
Ion actually said that change was “unintentional” and that they were “working on a fix.” And yet, it hasn’t been fixed (and probably won’t be).
I totally agree with your premise that items shouldn’t be changed after players have purchased them. But I feel obligated to tell you you’re tilting at windmills. Good luck though. Everyone should have a dream, even if it’s an impossible one.