I love changing the Battle Style to Set. Makes everything harder and more enjoyable.
That's an option stored in the save file itself, not the ROM. You'd have to find the routine that checks the flag for set/shift, and change it to always return set (ie no switch). Then you have to find that routine in the ROM itself and change it. A huge pain in the ass.
Nobody knows how to script events extensively, so rebattling things is out of the question for now. If only those drones at PokeCommunity would forget about that 7 year old game and help advance the newest gen for enjoyability.
Change the Marts to sell them is your best option. Sell different ones in different towns for whatever price.
See scripting argument above
@drayano
battle difficulty => difficulty value for the trainer