Tony
Actually, you can remove the tweeter grille without taking the midrange out. Its kind of a snap on device, so you will need to twist it with a moderate amount of force, but not something that should damage the tweeter in any way.
Then putting the new grille in place is easy.
Of course, removing the midrange is the best way to do it, but as I said, you can also manage without.
PS: Removing the midrange is pretty straight forward, so I would not be to worried of I was you..