Tier 5 - duration question

Found this informative site. This is my first post.

I wish to go to the UK or work attachment under an Approved government exchange program for two years under tier 5, but I wish to split this into 1 year of work placement then do a masters course under tier 4. After the masters I will continue my work placemet for another year.
The visa processing centre already informed that I have to leave the UK to change tiers.
My question is whether I am allowed to split the maximum duration of tier 5 into two 1 year stints. Or maybe it is two different periods of Tier 5 entries.

Hope this makes sense and u guys can help. Thanks