I can confirm that it is possible to change the cambelt on a D5 without removing the pulley.
I have done it on a 2006 D5 185 bhp and also on a 2005 Euro 3 163 bhp.
You cannot get the belt off with the pulley in situ so it has to be cut off and slid out. The new one will push back past the pulley with a little bit of effort and from there onwards you have it cracked.
On my current XC90 with Euro 4 D5 engine my belt kit came with a new crank pulley nut and the 4 small bolts as well.
I borrowed my friends ancient Ingersol Rand impact gun and the crank nut was off in seconds. Doing the belt with the pulley off is much easier and is the way that I will do it next time if ever there is a next time.
I bought a proper crank locking tool for about £20 and picked up a used monster Britool Torque wrench for another £40 so that I could accurately torque the new nut up to 300nm.
In short you can definitely do it with the pulley on but I would get the gear and take it off.👍