Should I change the Action to Reaction if I'm buying Enhanced Dodge/Parry?
No. It would increase the expense for less benefit. Reaction is meant to be used for powers that would normally take another action (like damaging someone who touched you, or emitting a psychic null zone when they detect the presence of telepaths). It lets you take a "free" action even when it's not your turn, but only under a specific circumstance (Triggered is a cheaper version that requires an action to "set", can be disarmed, and only works as many times as you have ranks in Triggered). Enhanced Dodge and Parry are Personal, require no additional action, and are just always there.
They might be Sustained, though, rather than Permanent, so that you can alt-effect off of them at the expense of losing that bonus if you're unable to take actions (at which point, you're probably already Defenseless, so no huge loss).