How to export RFC destinations prior Refresh

The best and easiest way...

Goto SE01, create transport request (Transport of Copies)

R3TR TABU RFCATTRIB *

R3TR TABU RFCDES *

R3TR TABU RFCDOC *

R3TR TABU RFCSYSACL *

If you take only RFCDES you will be missing the Documentation part of RFCs in order to take everything you need to have export of all the above mentioned tables.