You could start by inserting manual page breaks between all the pages. That way any changes in line numbering will be restricted to just the page you're editing. Furthermore, if you start making changes from the bottom of each page, the line numbers towards the top won't have been changed by the time you get to them. When you're done, delete the manual page breaks.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

That makes sense thank you, if I highlight changes as i go I can also then refer back and report to each reviewer "re comment x; please see line (new line numer)"

I'm going to merge their comments now and sort them so I can work backwards rather than going just going through reviewer by reviewer.

Thanks again, that lets me get on with it... in the meantime though, if anyone does think of a way to actually preserve the old numbering, (possibly even beside the 'new' line numbers which update as you edit) it's still bugging me!