It all depends. For instance, when using it with Pathfinder, I can easily create a customized magic weapon through the interface. I can also open up the HL Editor with the program and, with some coding, create new classes, feats and such that work with the program. It's not as easily customizable as something like HMP, but that's to be expected since building a character is a wee bit more difficult than building a mech. I suspect that the Shadowrun package will be a lot easier to customize than the D&D packages, however, since Shadowrun's character generation and maintenance is a lot more free-form than he Pathfinder/d20/4E rulesets.
