Changed the original post to this but wanted to make sure as many people read it as possible and know of the correction.

04/18/16 post update - Thank you Firetiger for the correction. I was wrong in saying - "I am 95% sure the rule is once you "possess" the fish it count's towards your limit and that's that... You can't then later, even a few minutes, toss it back and replace it with a newly caught fish, even if you are not at a full limit." I put the "95% sure" and "I don't have the regs in front of me" in the original post precisely because I didn't have the regulations handy and didn't want to say something for certain that I hadn't checked. This is a great example of 'check before you post.' I apologize to anyone who read the post before the correction and now thinks you can't "cull" fish in a limit.

Checked with ODW. It's been the rule / law for a long time. Don't know where the idea came from in my head, but I got it wrong. Maybe I got it mixed up with another rule. Anyway, yes you can release a possessed fish as long as it is alive and replace it with a newly caught fish. So if you already have a limit and catch "the big one" you can keep it and release one of your previously caught fish as long as it is alive. You don't have to be at your limit, you can do this at any point provided the released fish is alive.

However, as mentioned in the original post and commented on by pimplepounder, "fish involved in this process and later released have a high mortality rate... The fish may seem fine and swim away with a few quick tail thrusts, but the many stress effects of being caught and then kept out of the natural water environment take a hidden toll that often doesn't show up until later. So think twice before doing this, most likely you are releasing a fish that will not survive."

Just because a fish is "alive" doesn't mean it's good sportsmanship to release it in order to keep a freshly caught fish when it may be or is past the point of recovery if released. Each of us has to make that decision according to the situation, no matter where we are fishing.