I have performed all the tasks and got the system up and running, can I just change the SID on my new system?  I would have thought I could copy the domain users such as PRDADM to SDNADM, rename the oracle users, change the SID in the instance and oracle profiles and then in the environmental variables?

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"Renaming" a system is not supported officially and thus not fully documented.

It's not about just renaming a SID, SAP internally there need to be ran jobs (to create the "own" RFC destinations, jobs as RUTTTYPACT and others), create rfcexec.sec etc. etc. - those things are handled nicely by sapinst.

The system may work at the first sight but you will start getting trouble if you try to connect that system to another system using RFC (e. g. transports) because of a missing "secure store" etc.

The following places come to my mind where manual changes has to be done:

- profile changes (start- instance-)
- OPS$-user changes
- IGS RFC destination
- local filesystem permissions of the kernel files(if you change the user)
- operating system user permissions (speaking of gpedit.msc)
- permissions on registry keys (yes, they have also permissions) etc. etc.

As part of our upgrade we need to rename our existing development system from DR1 to DR2. What is the impact of renaming an existing system from an ongoing development/configuration standpoint? 

You need to change the SID before upgrade or after Upgrade through System Copy etc. There is not harm in changing the SID, make sure all the POST System Copy activities are carried out before the upgrade, eg. Instance Profile Names, etc.

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