I'm not sure, but I
believe you're asking if you retain your LS Mastery bonus when you transition from Sentinel to Watchman - if that's what you're asking, then the answer is yes.
Unless of course you do something DS and lose your Mastery bonus. I do this a lot as there are frequently times that it's just too darned much fun to do stuff that's technically "dark side"... f'r instance:
Spoiler:
On Dantooine when the mercenary tries to pick a fight with you, it's just waaaay too much fun to mind-control him, take his weapon, take his money and command him to never talk to you again. 