Hey there. Sorry for the late response; I was offline for a few days! I merged your two posts (first two posts by new members must be "approved" by mods/admins to publicly show-up on the boards), so feel free to edit out the duplication.
To your main question: I think this "exploit" might actually work: starting a battle on Hard to get more enemies (so +Renown from Kills) and then switch to Easy mid-battle to get the +2 Renown at the Battle Resolution screen

Do test it and report back if you find the definite answer.
Fighting lots of Enemies on Hard (w buffed stats and all) using Rank 1 Heroes can be... challenging, but not impossible. Several people have done that; do a search for "Lerajie" (or Leraje) power-save in Steam forums.