can the rear shock absorbers be replaced separately from the air suspension bag assembly.

how difficult is it to replace?

btw it is a 2004 4.4 v8

Looks like a straight forward job on Rave

Yes, they are a separate item.

One big bolt on the rear hub (wheel off, support the lower arm), three nuts at the top end (seats forward, carpet back).

The most difficult part is getting to the three nuts at the top as these are hidden under the carpet which is very very thick and sturdy at this point. Worth spending some time removing interior trim so that you can easily raise the carpet to reveal the top of the shock absorber, otherwise you may end up ripping the carpet in frustration (words from the wise, after the act!) .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

forgot to ask - would you use Monroe shocks or should i be looking for Bilstein or which brand would you buy - bearing in mind that I will most probably sell the car by mid-2014

I fitted a set of Monroe shocks to my Classic RR a few years ago and it was money down the drain, they were cheap and nasty and the darned RR drove like a plate of jelly. I then fitted a set of Bilsteins and the RR was transformed. If I were you I would try Dan for some genuine Land Rover shocks

Genuine every time