How difficult would it be to change the main diamond in my engagement ring?

It would depend on your engagement rings designs and creativity on main diamonds. If you want to change the main diamond of an engagement ring you should ensure that by whom you change your diamond he would be an experienced and expert one on diamond ring making. I also had a diamond rind ring which was offered by my husband to me before marriage on valentine day. That ring was shopped by online through the site as jewelrybyraphael.com. When that ring was not fit to my finger my husband was sold it because it would be more costly if he was repaired that.