If it is a CS position or any other non-management level position, you will have little success, but may be agency specific. At least with my agency, all CS positions are unions who set the standards for where new hires fall within the pay grade and then yearly step increases. No new hires are able to negotiate a different salary.

If management level, you should be able to negotiate successfully, pending the hiring department has the funds to give over the minimum starting. I was successfully able to negotiate for mine.