William, there are circumstances that yes, you can have orders cancelled. your command can do it by requesting a change in your PRD. Usually for exceptional reasons, spouse death, child's death, etc. It may not be true now, but when I was on active duty I personally knew people who refused oders. Requested a re-issue, and got them.
I went to medical, had a PFT done where they said my asthma was pretty bad. Had a follow up with my provider today and he starting talking about medically separating me for it.
there are circumstances that yes, you can have orders cancelled.
JPOPE, This is true, but the poster wasn't asking about unusual circumstances. In my 24 Years (17 as a PN) there has never been a time that a member can simply refuse orders. This has been a myth since I have been in that simply is not true. Orders can be changed or modified for a reason, however, "I don't want to be stationed at XX" is not one of them.