Hi,
The AD schema extensions are the same for SCCM 2007 as for SCCM 2012 so you don't have to extend it again. As long as you don't overlap the boundaries it will be fine to run a POC in the same AD as the production environment. I recommend that you use
a dedicated VLAN for testing, I do this kind of setups all the time.
Regards,
Jörgen
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