udevil seems to have it's config file hardcoded to /etc/udevil/udevil.conf, which is located in readonly system and from a quick glance there doesn't seem to be an option to override/change that.
But I've already opened a PR to drop mount_point_mode udevil: don't change permissions of mounted filesystems by HiassofT · Pull Request #3165 · LibreELEC/LibreELEC.tv · GitHub
Mounting some filesystem should never result in any modifications of it and doing a chmod() is a really devilish action of udevil.
so long,
Hias