I've just had to go through the introductions with my two neutered boys and their respective girlfriends so read up alot on it first.
The way I interpretted it is that if you keep introducing and separating then the piggies have to keep going through the dominance thing every time i.e they go back to square one.
From what I read it seams that as long as you throughly clean out the cage, houses, feed bowls, water bottle etc then introduce them on neutral ground before putting in the cage.
When you introduce for the first time it said to be ready with a towel to separate if things get heated. If no blood is shed then leave them to it in their new cage. They will go through the humping thing which is all part of the sorting out who is the dominant piggy.
Also ensure that you provide two feed bowls and two water bowls in their cage so that if one gets protective the other won't go without.
I followed this advice with my four and all went well. Expect them to hump for a few days (this is what one pair did) but they will sort them selves out, just takes some longer then others depending on the individuals personality.
However I am relatively new to piggy keeping (only kept them for a year) so am happy to be told otherwise!
I think the golden rule is that if there is no blood shed then leave them to it.