This idea is (almost) very simple, you give porkchops to zombie pigmen (3 cooked ones or 6 raw ones) they will turn into normal pigmen they would still carry swords, and could exit the Nether with you, but they would never come back to the Nether.
You also could give them armor, bows (no arrows required), new swords and radios!
You:But there isn't radios in Minecraft!
It's simple! First you has to make an iron rod (made same way as sticks, but with iron bars) and make the same recipe as the compass but puting the iron rod on the upper right corner like this:
Mushroom = redstone
Stick = Iron rod
Radios would be used to track their health and do squad commands.
You:Squad commands? da fuq?
Squad commands could be used to give them orders, such as attacking a certain mob in your cursor (they'll never attack passive and allied ones, doing nothing instead), telling them to move to a certain position, etc.
Some squad commands:
Take this [name of pigman](open your inventory to give an item from it)
Shhhh!(they'll sneak, hiding their names)
Some replys made you give them orders:
As you say!
(you'll need an radio in your inventory to give them orders)
Accidentaly hitting them will only give them half a heart of damage.
You will be limited to have 8 allied pigmen.
When replying they'll emit various oinks as the text appears on the screen.
You can also name them.
They'll would carry a 3x3 inventory which they would store items, and would also carry an equipment slot which you they equipment.