Ahhh - wrong terminology being tossed about here.
Hops have (as a simplified picture) essentially two components that interest us as brewers
Alpha acids - which once exposed to hot wort for a period of time, convert to iso alpha acids which give beer its bitterness.
Essential oils - which give beer its aroma
The alpha acids need time in the heat to be useful as bittering in beer - the longer they are there, the more they will convert, the more bitterness they will contribute.
The essential oils are almost the opposite, they are really quite soluble and range from very to extremely volatile and the longer they are in the hot wort, the more of them just evaporate away and contribute nothing to your beer.
So - an extra steep for your hops isn't about extra "isomerisation" or any process that is similar, its just that - well, smell the hops after a quick press.... They still smell plenty nice. Plainly some of the nice smelly stuff didn't get steeped away. So i have a second go. Its a plant, bits of it will come off easer than others. Quick action for the delicate fast evaporating stuff, a second crack for the more stubborn aroma compounds.
I more or less only use hop pellets and they work perfectly well in my press, you do lose a bit of liquid to absorption by the plant matter though.
This sort of technique really has nothing to do with bitterness - its about aroma. If you want bittering, add more bittering hops to your boil.
