Had a look at RD's site.
They have a "Bullet Assembly Plier" (pic below) which appears to be an aid for snapping in the bullets but I can't see how it can do disassembly ?
It can't. The dissimilar metal corrosion between the tin plated double female and brass alloy bullet strikes again.
Get a selection of bullet ends and the proper crimp tool, cut the old ones off, strip the wire, crimp on new one. You loose 1/4" in length, but you have a new, fresh (mostly) uncorroded crimped bullet on the end. Sometimes it's just easier.
When you put them back together, get yourself a bottle of Penetrox from the local big box hardware store of choice, smear a little on the bullet, and push together. Problem solved for the time you will own the car.
(side note...one of the reasons Jag electrical systems are so fragile is the number of those bloody things they used to connect the rat's nest of wiring in the cars...Lotus are just as bad...I could tell you stories of reterminating the entire harness from 693R back in '07...but to this day (AFAIK) the subsequent owner has not had any electrical gremlins...)