Can I make a pre-hung door jamb narrower?
Sure.


Remove the hinges and door slab.
Mark the location of the jamb stops with masking tape on each side, and then remove them by carefully prying them away from the jambs. They're usually nailed or stapled in place. 
Disassemble the jamb by carefully tapping apart and removing the nails/staples/screws at the corners. 
Run your jamb through a table saw, splitting it underneath the stop location. Run them through again to remove additional material to achieve the jamb depth desired.
Combine the two halves of each jamb component using wood glue and clamps. Allow to dry overnight. 
Reassemble the jamb corners using your fastener of choice, then install the stops, hinges, and slab. 
Hang the door as usual. 


However...

It may be simpler to just fur out the back of your door casing (trim) to accommodate the extra depth. If done well this is nearly invisible, plus you have the option to convert to drywall later without replacing the jamb.

Also...

It would have been prudent for the paneling installer to have furred out the wall framing to achieve the half-inch thickness for just the reason you've encountered. That's water under the bridge, obviously, but it's a thought for next time.