Many many moons back I was presented with a similar bit of paper to sign before I started a conversion course.
I never actually signed it! still went on the course funny old thing.
But 5 years left out of 12 is actually still quite a lot! when you signed up in the mob you were told there were no promises in where you would be posted, so that could include Down South as well as up there!
Ask the question, if you had not signed the RoS paperwork would they have sent you on the OCU back then? If not what would you have done? civvie street???
In our trades we are pretty lucky in we know there are a limited number of available postings, and am sure you knew the options when you joined
There are a lot of trades that get moved all over the country.
However, you can always ask the question of the desk officer and see what they say