When I export from 11.6 and import into 12.0 I get...
Import Error: This config file version 11.6 is not compatible with current import utility version 12.0
I agree you either need to hack the config file and hope that it imports everything correctly or you could, if you have a standby unit, upgrade the unit to 12.0 then export the policy and then downgrade the unit back to 11.6.
This is not the easiest way to do it but if you want to make sure the config file will be compatible it is probably the best way.
You attempt to hack this together by re-packaging the tgz file and updating the meta-data header to version 12.0.