@Ray, I think its not just backing up the server or so.
Like what i have experienced, You just need another copy of the server and run it with the renewal client. (everything is the same except for the client)
Explanation: Finding new stable client is not that easy (2012 clients is the stable one "Like they've said") *repacking .GRF files, LUA files and friends, Translations from Hangul to English, New Client Packets* and for the server, some configs (Not as hard as the client thing) I've running an offline server recently, *not the eAthena* and just blowed my mind migrating from old Ragexe to new Ragexe which is the renewal GUI (Lot's of thing you need to do Like "RENEWING YOUR OWN kRO GAME CLIENT and download a 2gb file for that") *its been running :)*
About the said renewal Client "w/o" 3rd job: Yeah its possible! The only come up of that is "Job Kafra" *blame her if she run the script to change characters into 3rd job classes :P*
Edit:
Anyway, as for me, i can provide the server a renewal client GUI but its not that easy working on the other side of fRO :), they we're the only one who can do it :).