Using the bat file command method in Post #3 only replaces your primary detail map [gmapprom.img] in region 49.

MapInstall does not detect maps on the unit, only BaseCamp can do that provided the MS Flag is '0' as said before. If you have generated an image to a card or USB stick from MapSource or MapInstall with the intention of renaming the image from gmapsupp to gmapprom before transferring it to the SP using the bat file method, you have the opportunity to change it to '0' at that point. Once it is on the unit you cannot change it. Similarly, if you use MS or MI to transfer a secondary detail map directly to the unit as gmapsupp it will have a flag of '1'. The way around that is to also first generate the map to a usb and change the flag before transferring it to the unit via SendMap20. Regardless of where you source the image from, compiled yourself or downloaded, it's necessary to check the MS Flag before putting it on the unit if you want BC to see it that way.

If you wish to erase gmapsupp you can do that with SendMap20. You could also overwrite it with a single small tile from MS or MI so it's only a very mall size map. I don't know if you can simply erase gmapprom although i haven't given it any thought, as i don't see a need to do that anyway because you would always want to replace the primary detail map for sure anyway.