You don't have to "register" at all. IF you were a contractor applying this on someone elses land, you would need to be certificated for a PA1 (foundation module) and a PA6a (hand held applicators module). However, as you're using this on your own land, you are ok.
As far as i'm aware, there's no such thing as "farmers strength" roundup (although i stand to be corrected) and the farmers strength is dependant on dilution rates....roundup can be used virtually neat for stump killing.
I have both the above certificates as well as PA2a (tractor mounted sprayer)