I've never done the EGR either, the guy that writes that site is a Volvo
mechanic, if he removes the throttle body, I'd say there's a good reason
for it.  I'd think that reason involves access to the bolts, cleaning
the hole in the manifold, or cleaning the throttle body while it's off
is part of the service.  Try doing it your way, see what happens.
Personally, I'd remove the throttle body, while you're there it's a good
opportunity to clean it.

Assuming the used EGR valve opens with a vacuum applied and closes
tightly when the vacuum is removed, I'd probably try the used one.