I’ve done this recently where there was some pretty wholesale changes and cleanups made to an existing site. I pulled it down, set it up in a local dev environment with a dev.example.com type domain name that was also accessible by the client from the outside for testing.
This allowed me to still refer to the existing site should I need to, and identify the entries that had gone in since the site was pulled for the major update. I tried the couple of the export/import tools when it was time to go live, which I stuff around with no success for a couple of hours. I then did the work manually, in my case there was only about 10 new entries, which took me about 30mins to bring across, back date and categorise (I had new sets of categories too).
You’d need to look at it on a case by case basis I suppose. If the webmaster is going to be updating many times a week, then potentially have him enter the entries into the DEV environment at the same time. The main problem will come where there’s comments involved…luckily I did not need to concern myself with that. In my case also, the export/import tools were for EE v1.x, so the landscape on how successful the equivalents are for EE v2.x I cannot comment on.
If you’re only doing changes to parts of the website, that only you want to see the results of in the LIVE environment, you could potentially just use a conditional:
{if logged_group_id == 1}
{!-- my new code variant here --}
{/if}
Hope that helps.
Cheers
Brendan