So many sounds can't be modified at all.
If you're referring to the E-A7 I find this surprising Dave. Pages 29-33 of the Reference Manual imply that you can do a lot more sound editing on the E-A7 than you could on any previous Roland arranger.
I'm not into sampling or creating my own sounds. But with that kind of editing ability and so many base samples to choose from, I would think that the E-A7 is pretty good in this regard.