There is no known way to downgrade the software. Once you update to software version 0330 or newer (with Euro DVD 2005_1 or newer), you will not be able to use older original DVDs or copies of the 2005_1 or newer DVDs. IIRC this is also printed in big letters on the 2005_1/2005_2 DVD cover.
At this time your only option is to get your own original DVD to use in your RNS-E.
At this time your only option is to get your own original DVD to use in your RNS-E.