For some reason I always assumed that when Darkseid put Lionel's heart into the Lex clone that he put Lex's soul
back in as well. I suppose that was just my own poetic musing on the whole matter though.
There seems to be more
Lex than he just being a biological Smallville: The Best of Lex
He seems like the real deal. Memories don't make the man after all. Take Connor for example. All of Lex's memories but who did he turn out like? Clark!
Of course that's just my opinion so take it with a big ass grain of salt!