But I think since I’m editing a plugin file (user/plugins/tntsearch/pages/search.md) it could be overwritten in a future update of the tntsearch plugin. The perfect solution would be one that can continue to work when the plugin is updated.
In Customizing the Search Page it is stated that the plugin uses the search page it provides if there is no physical Grav page at the search path route. So, I assume that when you copy the plugin’s search page and make that accesible through the (configured?) search route you are set.