You can still specialise as a CSO. I know someone desperate to join the force, but couldn't get in, so became a CSO. Once a CSO he did all the training including his firearms training, once he had that he got a job as an armed guard at a nuclear facility somewhere, still CSOing in his spare time, evenings and weekends on the streets. When off duty he still had the skills as they're not attacthed to the uniform. He then get into the force in Northampton. Moral is, if you want to be a policeman, go to Northampton...no wait...