Thankfully someone else has the number 10121 as standard, I changed mine from 10121 to 10151 and as soon as I rescanned it came up as 10121 so I turned off the engine, turned on the ignition, changed it again and voila, accepted, not really noticed a difference TBH, might go for 161 or 171, see how they feel.
I'm also having this problem although even after switching engine off and back on again i'm having trouble changing some codes?