The Joe Bloggs people cannot be edited to be in the game.
I already tried copying a player over a Joe Bloogs but it doesn't work, even with changing the Player ID.
There are several attributes which I am yet to work out what they mean and are hidden, so, when creating a new player (such as Tremlett) I suggest you find a player with similar bowling style, batting style, etc. and then copy and paste him over the player you want to replace.
As for the names issue, your game profile stores all the names as well and overrides the file which my editor changes. So you'll just have to do it yourself unless you want to delete your game profile...
Sorry!