You seem to be doing an awful lot of work if all you want to do is incorporate RollSnare into your kit. The RollSnare sound is already present in every kit on C#1 (one octave BELOW the regular snares). Using a drum track in Cubase, you can simply select any unused drum in the list, and change it's "O-Note" setting to C#1, (and then you can rename it to "RollSnare" if you want).

If you need further help, please let me know. I could explain how to do it with the performance edit method as you requested but this way is much more foolproof (it works with the standard drumkit instead of needing to load a special perf).

Chris