Your favourites are kept in a file called mapsettings.cfg and it is stored in the specific map folder. So, you can try copying it from a backed up map to the new map folder.
What many do, however is to download a program called poiedit from PoiEdit - Main, load the mapsettings.cfg file into the program, save the favourites as poi locations and store all the (new) poi's in a custome poi category called whatever you want. Some suggest a name like _my_favourites.ov2. The initial underscore ensures the new category will 'float' to the top of you poi category listings.
Now then, all custom poi .ov2 files (and associated .bmp files, if you have them), sometimes automatically get retained in the map folder as the installation process overwrites new data over old data in the various files in the map folder.
But, if this process did not take place, then simply copy your custom .ov2 files from the old (backed up) map to the new map folder.