Just an FYI, it’s generally recommended to make that kind of change in a small theme component so it can be used with remote themes, as well as being attached to multiple without editing each separately.
Though I think it’s worth checking whether this is a sensible limitation to apply in the first place. Having a customisable navigation menu per user so they can adapt it to their own tastes (or leave the site default in place if preferred) seems like a massive plus point.