As far as I'm aware, if it doesn't specify which decrease, you can use whichever you like. I use K2tog, but it doesn't matter. :shrug:
To reverse shaping, just swap which side you do all the BOs, decreases, etc. on. Your right front will be a mirror image of the left front. For example:
- Left front: you bind off stitches to start the armhole on the left side of your piece.
- Right front: bind off the same number of stitches at the same place, but on the right side of your piece.
Hope that helps!