You can do it with a 60CSX like this. From the map page press the menu button, then right or left arrow to the “i” icon in the circle. That gives me a list of all the individual map sections on my GPS. You can turn them on or off by selecting the map name and pressing enter.

Pressing Menu again lets you turn off an entire map “product” like “Homemade maps” or “City Navigator”.

With luck you’ll find an analogous solution on your Etrex.