I have a realm world (I am using the free trial, if that makes any difference.) which has commands enabled. I downloaded the world, which automatically turned into a single player world. When I went into the single player world everything looked the same, I even had the same stuff in my inventory that I did in the realm, but I only had access to commands such as /me, /help, /msg, etc. But, I didn't have access to all the other commands (/fill, /give, /weather clear, etc) and I wasn't able to edit the command blocks that were placed down. All the command blocks still worked. I looked through the settings, but I couldn't find a way to give myself access to the rest of the commands.
I realize I could just finish the commands on the realm then download the realm world again, but that would mean I would have to finish all the commands for the map I am making before my free trial of realms runs out.
This is not a huge problem, but I still hope there is a solution.