Title 5 authority only (pharmacists are Title 5 for this purpose).
No longer on reapply between GS jobs, repealed during the Bush Jr. administration, and it only applied to CSRS staff. Knock yourself out applying to other jobs. Now, between GS and uniformed/NSPS, there is a rule, but it basically is that you get the lesser of the two compensation schemes.
For "cannot leave", you have to sign a retention agreement and you can ask HR if you have one (EDRP is the most common and PCS the second most common). I've never heard of a situation where a retention agreement was not exchanged for some consideration, usually a pay bonus.
The rules are different for Titles 10 (Uniformed and their spouses), 38 (VA Clinicians), and 42 (HHS), and I know for 10 and 42 that there are rules about job switching that do have limitations.
If you are going into an NSPS job or moving to Falls Church or Meade, I just want to warn you that you're financially better off not switching. Only do those type of jobs if you really have a deathwish.
