Changing a DHCP Scope

I have three current scopes 10.10.1.0 this is the corporate office, 10.10.5.0 and 10.10.10.0 All using a 255.255.255.0 mask. We have been acquired by another company and our 10.10.10.0 range is already in use by the other company. They wish to change this scope to 10.30.23.0 with a mask of 255.255.255.0 we also need to maintain connectivity with the other two scopes for the time being. What is the best approach to setting this up with the minimal amount of headache? All servers are Win2k3 and clients are XP pro
Thank you
Ken