This is potentially dangerous.
You may do what you like with your system, but, please, don’t advise others to do this.
There is a lot of misunderstanding with when and why mirrorlists need to be recalculated.
The most dangerous part is assigning this important system task to an automated procedure.
When you change your mirrorlist(s), for any reason, you need to refresh packages and immediately update the whole system.
Since you can’t update your system unattended, you can not automatically create a new mirrorlist.
If you want better options to ensure your mirrorlist(s) are always proper (not updated), try safesync (it is recently added in chaotic).
Because safesync has a lot of functionalities, I suggest you study and experiment with it (if you actually want to safeguard your system).
I would appreciate any feedback, either in a new topic here, or at GitLab issues. 