Correct me if I'm wrong, but with the new rerolls already do critical confirmation. My macro for attack is [/r 1d20r20+@BAB+@STR+@MISCATTMOD+etc.] So when the dice doesn't come up a 20, it adds as normal. When it does, it rerolls the die but only adds the modifiers to the second die. This is copied from the chat log: rolling 1d20r20+4 +2 +1 +0 (20+6)+4+2+1+0 = 13