I can't guarantee the fix to be perfect, but I think I got all of the vandalism: I did do some validation fixes as well.

Hello, having got a second opinion by nikospag at https://forum.openstreetmap.org/viewtopic.php?id=75599, sadly I had to revert changesets 121113946, 121018248, 120970818, 120942371, 120941864, 120936058, 120934012, 120933718, 120903247, 120895348, 120895091, 120894913, 120894823, 120890561, 120890170, 120853752, 120852593, 120852413, 120851514, 120848149, 120848072, 120847905, 120847696, 120808608, 120808470, 120808296 and 120808111, because they did not reflect the reality on the ground or in legislation.

Next time, please check out our extensive documentation on the highway network at osm.wiki/Greece/Highways.

If you have proposals for large-scale changes to the numbering or classification, you should start a forum thread at https://forum.openstreetmap.org/viewforum.php?id=27, instead of just doing it yourself.

Finally, please use proper changeset comments instead of just typing random letters.