All went smoothly, but now my remote base stations (I have a WDS daisy chain 4 links long - see earlier post) don't show in Airport Utility. Still connected - I can ping them just fine, and the remote airTunes express shows up in iTunes.
Update this seems to have been a temporary problem. Everything is now visible again.
All my airports (7 at last count) are configured in bridge mode - my speedtouch adsl modem router provides a DHCP server. On the bright side, this update seems to have helped with one issue: the 802.11n extremes now seem to pick up an IP address from my router using DHCP (previously I found this didn't work and had set manual IP addresses as a work-around).