Can I convert jam into chutney?
Perfect idea and great multi-use of your jam!  Your plan is perfect...just create a nice sweet tart balance to your liking.  If you want a little more texture you could plump up some golden or dark raisins by nuking them in the microwave before adding.  Coriander seed is often used and provides a little texture contrast as well.  A bit of ground allspice could be good as well.