I have a tiled bathroom which has a single switch for the light. I'm
installing an overhead light and a fart fan, and need to add a bigger switch
box. The problem is the box would be in a tiled area, and I can't just rip
out a couple of tiles and cut new ones to fit (I don't have any matching
tile).

So, would a rotozip or equivalent work to neatly enlarge the existing hole
through the tile.

Is there a better way to do this? (Remember, I don't have any spare tile,
nor do I know what grout was used when the tile was installed).

Thanks in advance...

KB