How to perform a non-destructive email routing test prior to decommissioning Exchange 2003 from Exchange 2010

Before decommissioning my Exchange 2003 server, I want to test email routing as if the Exchange 2003 server no longer existed. I want to do this without deleting the RGCs that were created during install but I’m not sure how best to do it and looking for a process.

Could it be done by setting the cost of the each directional RGC between EX2003 and EX2010 to something like 50 and using my send connector “Internet SMTP Connector” to route email out of EX2010 to my perimeter (local) email gateway appliance? My send connector looks like this:

Name                  : Internet SMTP Connector

AddressSpaces          : {SMTP:*;1}

HomeMtaServerId        : srv-ex2003

MaxMessageSize         : 25 MB (26,214,400 bytes)

SmartHosts            : {[10.21.21.1]}

SourceTransportServers : {srv-ex2003}

Would I have to alter SourceTransportServers and HomeMtaServerId values?

Thanks.

Kevin