looks it is worth updating.
you will be able to change your existing rom to free play just by changing the pricing settings in the "Pricing Adjustments" to free play

on most revisions they have fixed problems

the list below explains what they have done in each revision

H-4           May 24, 1994    Changes from Revision H-3:  [RECOMMENDED]
                               - More display stuff fixed.

H-3           May 6, 1993     Changes from Revision L-6:
                               - Updated operating system for new slam tilt switch handling.
                               - Re-added "Home" settings from Internal L-7.

L-6           Mar 18, 1993    Released only to a German distributor.
                              Changes from Revision L-5:
                               - Updated operating system to support a new printer type.
                               - Non-working "buy-in" option added
                               - Only two champions displayed instead of three as in L-5
                               - Change in default high score credit awards

L-5           Dec 9, 1992     Includes all changes up to Internal L-8, but had "Home"
                              settings from Internal L-7 removed.  At this point, the
                              large score font was changed to be conditionally compiled
                              only for Home ROM versions.

L-8           Nov 8, 1992     (Internal testing only, not released.)
                              Changes from Internal L-7:
                               - Updated operating system for improved coin switch handling.  
                               - Cleaned up some more display stuff.

L-7           Oct 15, 1992    (Internal testing only, not released.)
                              This version likely came into circulation during Pinball
                              Expo '92, when it was handed out to a few people as a "Home" version.
                              Changes from Internal L-6:
                               - Added adjustment "GAMEOVER KICKOUT"  
                               - Added adjustment "FREEPLAY MESSAGE"  
                               - Added adjustment "SPOT GREED/BALL"  
                               - Added "SPOT T-H-I-N-G" for a different rule that was
                                   added for spotting THING letters.  
                               - Added "INSTALL HOME" preset.

L-6           Sep-Oct, 1992   (Internal testing only, not released.)
                              Changes from Internal L-5:
                               - Added soft firing of ball release on swamp release coils.  
                               - Added large score font.  
                               - Cleaned up some more display stuff.

L-5           Aug 3, 1992     (Internal testing only, not released.)
                              Changes from Revision L-4:
                               - Cleaned up some display effects.
                               - Fixed a problem where "thing awards" could not be collected
                                   during Tour the Mansion if Quick Multiball was lit.
                               - Jackpots are now awarded during multiball if the ball makes
                                   it into the vault (Dirty Pool).

L-4           Apr 27, 1992    Changes from Revision L-3:
                               - Changed default German pricing.