You mean that you have option to change navigation path manually, but you cannot change it after you insert SD with new navigation app? Or you mean that you don't have that option at all and you still want to change/start new navigation app? If that's the case, than all you have to do is to rename the navigation folder and executable file as it is in original. Simple as that. I hope you understand.
A further development: Just as digging about, trying to understand this SOB, I copied the backup (I always make a backup before toying with new apps) to a new sd card and I could set the nav path SDMMC\Primo IGO9\iGO.exe no problem. Guess what! When selected from the main screen it looked as if it would run. .... then froze. Tried reformatting the card recopying the whole process but still the same.