Trying to sort this out before my inexperienced wrenching messes something up. I have swapped freehub bodies on 2005-prior Campagnolo wheels out, and it takes about 30 seconds.

I have a pair of 2006 Campy Eurus wheels. The new freehub body and pawl carrier is housed differently, in one big Al piece, and you've got to take apart the entire axle to get it out.

Once I've done that, though, does anyone know if the actual freehub body is the same under there, and can be swapped for a pre-'06 version?

Good question. I'm thinking of getting new Eurus wheels, and I have a couple of Record hubs, so there's my interest.

The part numbers for the 2007 Record hub and the 2006 and 2007 Eurus freehub bodies are the same: FH-BO015. I checked the 2006 Record hub - it has a different number: FH-RE415. Campy states that the new bodies are only compatible with the new axles, so it seems to me that the new body can't be placed on the older hubs. And the reverse appears to be out of the question too.

I posed this question to Campagnolo USA, (or North America now), when that new lighter one piece freehub first came out.

The freehub has to match the axle. You can put the new one piece freehub on an older wheel or hub, but you would have to change to the new style axle.
The newer axle uses the same cones, bearings, races and seals etc. as the previous years axles.
It looks like you can do the reverse as well, but not sure why you would do this other than for a repair issue.
If you look at Campys spare parts pdf's for the 06 Eurus wheel for example, in the lower right hand corner, there is a note that points this out.

One other note: the new freehub says it requires a new specific lockring.

argh, that's kinda what I thought.

Why would I do this? Because I've been running campy stuff for a while, but my new bike is SRAM-equipped, so I want to just keep using my Eurus wheels...

At least the new one piece freehub wholesales for 40% less than the previous style. Thats if you compare old Record to the new Record "level" FH-BO015 which is the freehub on the Eurus wheel. The HG 10 version is currently in stock at one of the larger distributors.

Thanks, I'll look into it. I WAS thinking it not worth the bother, 'cos the old Record freehub was >$100 IIRC...