umm, I really don't understand how this habit can transfer over through series of games, but...try this:
Go to training mode and play against 3 snakes. Have them set to lvl 9 and put them at like 300%. They love to stay on the ground, so using dsmash will become instinctive once you us it so much. Just keep trying to kill them normally, and you'll realize that it's impossible to kill them efficiently w/o your awesome dsmash. Hopefully, you'll create a habit that's not as bad as the one you've got right now. (Kinda like smoking mary and then switchin over to crack cuz it's not as bad for you...)