debug. There should be an shortcut called debug, start the game with that. While in the game, open the main menu and select "Debug", from there choose "Pokemon options", then "Shadow Pokemon options" and then finally "Toggle Snag Machine".
This will allow you to catch shadow pokemon in trainer battles. If you don't want to fight them at all, add some Ultra or Master balls to your inventory and just immediately throw the ball as soon as they appear.
Wish I could tell you, but I pretty much stop caring about regular pokemon as soon as I gain access to the hybrids.