A quick Pic-tutorial.
G1 hair is easy to reroot--usually if you give a plug of hair a good yank, you can pull it right out. But G3 hair is liberally slathered with glue on the inside of the head and I have not had much luck pulling it out from the outside (or the inside, for that matter) so that it's in useable condition.
But there is a way to use it . . .


Things you will need:
A rerootee pony without hair
A donor pony with hair
Pliers
An Xacto knife
A big-ass needle
Matches
A candle
(You do not necessarily need to remove the head from your donor pony, but you can.)


Okay, so you've got your donor pony. The first step is to use the needle to separate out a single plug of hair. (In this case I'm only after the green hair. Otherwise I'd start from the very front of the hairline and work my way back.)


Next, use your Xacto knife to cut out the plug. (But be careful, Xacto knives are incredibly sharp.)


Now that you have the plug cut out, hold the cut end near the flame of your candle. The synthetic plastic will begin to melt. The melted plastic will hold the entire plug together. (As always, be VERY careful around open flame . . . No custom is worth burning the house down for.) The hair may catch on fire if you hold it too close, but don't panic, just blow it out.


Next, thread the hair plug through the eye of your big-ass needle (the more big-ass the better) so that it forms a loop, as shown here.


Stick the needle through one of the hairplug holes in your rerootee's head. (I always work from the front to the back of the hairline.) You may need a thimble or pliers to get the needle in.


Next, anchor the end of the plug with your fingers and pull the needle all the way out with the pliers. It's very important to anchor the loose end of the plug, or it will come right out with the needle!


After pulling the needle out, the hairplug should remain in the hole. Gently tug on the hair until the waxy end is right up against the hairline on the inside of the pony's head.


Repeat.
~LM~