Possible to do with the (I think) X9/X10 are the only routes that follow the exact same route but come of at different points.

The X10 covers the X9 route on evening and Sundays anyway so it's easier for GNE to withdraw the X9 (if needed) and shove the X10 to serve both routes.

I can't say the same thing for different routes. Maybe the 12/12A