I’m aware the generated maps at http://garmin.openstreetmap.nl/ have the same ID and that this can be changed using the JaVaWa GMTK tool. From the comments here in the forum and at other web pages, that seemed do the trick.
However, even after changing the ID and renaming first map via GMTK, the osm_generic_windows.exe for the second map prompts “OSM generic routable is already installed. Click
OK to remove the previous version and continue installation or
Cancel to cancel this upgrade.” And the OK / Cancel buttons do exactly what it is said here (even if it is installed to another folder, the original one gets emptied).
This seems as a standard Windows installer check which is understandable. This is caused maybe because GMTK does not rename the uninstall info for the map in Windows registry (located at HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall\OSM generic routable).
I can imagine one could install NSIS, load the tiles instead of the installer exe, patch the script to rename the app, compile it and use the new installer. Or, it might be also possible to patch the registry.
Is there any recommended way how to have two user-generated maps installed in parallel? I do not mean to install several country maps and compile the gmapsupp.img in Mapsource which would also work; the possibility to have several small individual maps seems more pleasant for me.
Selecting a name for the created map at http://garmin.openstreetmap.nl/ could solve it even if all the maps still have the same ID as that can be changed by GMTK (it would also be nicer to see the name in the device instead of the generic one). But I understand such feature has a low priority for the authors.