Hi, I managed to get my DS412+ running as a DS713+ on DSM 7.0.1-42218 Update 6 version. The proven procedure of @DSfuchs works just fine (Thank you) !
After that I tried to manually upgrade to DSM 7.1-42661 Update 1 but that fails with error: Incompatible Upgrade File.
Any suggestions what to change to make it work ?