Forum:2nd Playthrough on Same Character ME file transfer

Hey I created this account primarily to ask this.

As useful as the wiki has been there's something I'm not certain of. If I play my second playthrough on existing character, do those decisions override those of my first playthrough with that character? Or when I import over to ME2 will I be able to choose between the character's first 50 levels and relevant decisions, and his level 51-60 and relevant decisions?

Not really on-topic, but do you get more exp for assignments etc the higher the difficulty is?