I over-wrote them using Modify Player, changed their Position, Appearance and some of their more obvious skills/weaknesses.
No science to it really. The furthest you could go would be find out what PES2 had for their Stats/Abilities directly from an old copy of the game, or maybe some old PES/Championship Manager conversion page. There are one or two around, try Google.
If Hierro's a free agent in Master League, I think you'll need to buy that option in the Shop before you can put him into a team (instead of an existing player) using Team Selection.
That or make a 'twin' Hierro: using Create Player, then Base Copy the original. But created players are a pain, I find it preferable to edit an exsting one. Each to their own.
The only way I can see of getting an Adams or the like into the game would be either over-write one you don't want (like some the the crud DF's in Classic England's default team), or create a new player.
Have a look at
'Tutorial 7' - Transferring players in WE7. It's under the Patching Tutorials available from PESInsights main page.