The IDs are unique to the tiles on your dashboard so the IDs themselves won’t change, but we may change the DOM structure in the future. For example, we’ve been considering getting rid of the wrapped ‘tile holder’ as it was originally in place for a different reason and isn’t needed anymore. As such, you might consider using the .tile[data-entity-idx="XXX"] selector instead of the #tile-holder-XXX one.
Another approach would be to use the “named styles” approach where you would create a few different named styles, then you could apply the relevant style to the navigation tile in each dashboard and write your Custom CSS accordingly. .