Its actually model specific. You can take the GEM from one focus and move to another.
The program is only required if you take the GEM lets say from a LX Focus and move to a Titanium. As certain features are turned off.
That's why if you have a LX you place a Titanium GEM in you unlock features you would have never had before.
Programming is just a list of features that are meant to be on or off, that's how the Elmconfig cable works.
This thread may be old but just needed to clarify what actually happens. You can put replace a GEM best idea is to replace with a car with more spec or same as yours not one that is lower spec or you may lose features and then you will need the program to enable them.