I just got my 827h and was able to do what you need to do. However, since I did not use the built -in internal address of 10.10.10.1, I added the new ip address's network to the access-list that came in the default config - I believe it is 10 or 111?
My unit is at home otherwise I could be more specific.
Its the access list that permits incoming packets from the 10.10.10.0 network.
Anyway, in addition to changing the 827's internal ethernet address, add the internal network to that access list - then the web setup should fire up no problem.