Probably best to back up the data on your card before you begin writing other mapping to it.
Have a look on the card, Garmin mapping tends to be stored in two formats on their units with internal memory (and my old i3 with a data card does the same) and are named 'gmapprom.img' and 'gmapsupp.img'. If you write to the card from Mapsource you will create a 'gmapsupp.img' file. This is supplementary mapping to the primary mapping 'gmapprom.img'. If the file already exists then it'll get overwritten, that's why you should back up your card.
Both files can be renamed as the other so you can create a new 'gmapprom.img' file be creating a 'gmapsupp.img' from Mapsource and renaming. However you can only do this if the mapping in Mapsource is fully unlocked to your GPS.
The safest way, as others have said, would be to use a different card for your Morocco mapping.