Is it possible to replace the alternator clutch pulley without removing the alternator?

The short answer is - yes it's probably doable. This guide is for doing it on the XC70 2005 with D5 engine. But it is in a tight spot, so you should at least remove the cover around ECM/TCM. The best thing is to also remove the ECM/TCM-computers. You will need a special tool to remove the computers.

To unscrew the pulley you probably also need a special tool set like this:

Then you combine the two needed splined tools in the set:

Remove the alternator belt and the pulley cover. Insert the tool into the pulley. You have to loosen the AC pipe to get access.

Use a big wrench to secure the inner part of the tool, and a small wrench on the outer part of the tool.

Then remove the pulley by turning the small wrench anti-clockwise. You have to use a lot of force. You probably need a very long pipe that you insert around the wrench.

Then you replace the pulley with a new one by doing the same thing in the reverse order.