[Paro]

Questo http://www.javawa.nl/gmtk_en.html fa al caso tuo:
"Change map name and ID

A site like the Worldwide routable Garmin maps from OpenStreetMap is ideal to generate useable maps for your Garmin (and MapSource or BaseCamp). The major drawback is that when you download and install a second map from this site, you will lose the first one.

The problem is that each map has the same ID and name, while these need to be unique.
The problem with IDs in general is that there isn't a centralised registration and distribution of them; every map maker can pick their own, resulting in the existence of double IDs.

Luckily it is easy to correct this with JaVaWa GMTK, enabling you to use several maps from the source mentioned above (and others)."