I need to replace the radiator on my 2000 XK8. The workshop guide says to pull the radiator, fans and condenser out as a unit, opening the AC system in the process. I hope there is a way to remove the radiator without having to break open the AC system. Hopefully someone had done this and avoided the AC issue.

You can unbolt and remove the fan shroud assembly from the radiator but the problem you have is in order to remove the AC unit from the radiator you have to have them out of the vehicle. The AC unit is bolt to the radiator on the front side. They have to come out as a unit and then be separated.
Got JagRepair.com - Jaguar Repair Information Resource and download the 1999 second edition of the tech manual it is PDF searchable and you can visually see how the AC is bolted to the radiator.

when I replaced the radiator in my 2000XK8 - I was able to remove just the radiator and not touch the AC system

There's a metal shroud attached to the RHS of the radiator (#2 in the attached) which you will need to remove as it encloses the A/C lines.
It's held by two torx bolts on the front but they are a fiddle to get to.

Good luck.

#2 in the diagram is a bracket that holds tubes connected to the condenser. I didn't find it too hard to get to from the bottom front. I couldn't get to it from the top. Also loosen the other clamps for the condenser hoses near the radiator, and also the drier/accumulator, that will give you the wiggle room you need. Note that the transmission cooler inside the radiator holds about 1/4 cup of fluid as I remember.