If you’re running a mixed environment where you have Windows Server 2003, 2008 and 2012, can you manage Group Policy in this side-by-side environment?
Yes, but it’s important to note that in Windows Server 2008, Microsoft introduced a central store (to avoid GPO bloating) with ADMX and ADML templates to manage your Group Policy (GP).
Windows Server 2003 (ADM Templates)
Windows Server 2008 and higher (ADMX and ADML Templates)
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Question:
Can you run two GP environments side-by-side (ADMX/ADML and ADM) without causing problems, and is this supported (central store and ADM)?
Answer:
Yes, but ADMX template always win if in conflict with ADM.
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Question:
If we start using a central store and manage our custom ADM through higher OS level would this jeopardise any configuration on the existing ADM’s?
Answer:
No, this will be fine.
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Recommend Approach:
The best recommend approach is to move ADMX and migrate the ADM to ADMX using full armours ADMX migration tool.
XML-based format with Full Armor’s release of the ADMX Migrator tool, which Microsoft has licensed and made available through the Download Center. This tool provides a mechanism to convert your existing ADM files into ADMX format via a simple but effective user interface. This tool can also be used to create ADMX files afresh, which means you now have a way to create ADMX files without needing to understand the underlying ADMX format.
Links:
ADMX Migrator: https://www.microsoft.com/en-us/download/details.aspx?id=15058
Group Policy Team Blog: http://blogs.technet.com/b/grouppolicy/
Shabir Yusuf 