there is a way. search for "wiemdzmin" on forum. it allows to extract needed files from .bif. then you'll have to find a file responsible for xp gain and modify it.i dont have detailed answer how to make this mod but i know a bit about witcher. first time i hear about lower exp rewards on high difficulty. its easy to check it yourself, start game on easy and play 10 minutes in prologue. you'll notice that each killed bandit is worth 10 xp. try it on hard and you'll get same 10 xp. maybe there is a difference somewhere but i never noticed any. even if there is a difference, there are numerous unlimited spawning points in game. if you like grinding and power-gaming you can kill enemies up to lvl 50 and more. thats why some poeple finished the game on lvl 30, others on lvl 50.also if you want any challange, picking medium difficulty for (supposedly) higher exp gain will make the game twice less fun. it will be easier because of enemy stats and easier because of higher lvl, thats mega easy. hard difficulty is still VERY easy for any experienced rpg player. you dont even have to use 90% of geralt equipment. no salves, bombs, whetstones are needed. you need 1 or 2 eliksirs and thats all. you can stand in the middle of 10 drowners, leave computer for an hour, come back and you'll be full health.in my humble opinion, dont even consider taking medium difficulty if you want any challange in game.