Is there a way to appeal your reentry code even after being discharged for several years?

You need to talk to a Service Officer at a VFW or AL. Depending on the length of time since discharged. 15 years is the difference between who handles the request and the forms necessary to apply. In all cases documentation is king. I had a DD-214 corrected for a missing CMB by supplying a copy of the orders. You might want a records dump from the National Personal Records Center - ask for a copy of your "Official Military Personal File" to get everything about schools, deployments and changes in grade / pay which might reflect Nonjudicial Punishments. This is the stuff that the review boards are going to look at so you might as well get a heads up. If you want some more info feel free to contact me or post the question here. Good luck with your efforts!

PV2 Andrew Schauf- Anderson you can. It is hard to prove, though. I found that it was easier to go for a waiver for the RE code rather than to get it changed. They just simply asked for the impossible in order to get it changed - by impossible, I mean, even though I had gone through several doctors & even volunteered to appear before the Med Board to get it changed, they still rejected everything. I put in all that effort w/ absolute Zilch to show for it. So, I found a recruiter willing to fight to get me a waiver. Probably your best route, depending on what the reason for discharge was.