First, here is your answer: Oddly we had this discussion already in a thread here today. When you have action, if there is a pitching change then your wager changes. You wager changes to the opening odds of the new pitcher and your 'to win' amount changes but your 'to wager' amount does not.
If there is no pitching change then your wager is exactly like a listed pitcher play which locks you in at the odds you got at the moment.
Second....there is no reason to ever ever ever do 'action' that I know of.
If this doesn't make sense, let me know.
Good luck.
tulsa