I don't have time to explain how, but this is probably an exercise that is worth learning how to program the APIC using the APIs.
There are a couple of approaches, such as PowerShell scripting and using Python. Cisco supply a python library called Cobra that eases the pain of programming using Python, but if you are not familiar with Python or programming, this whole task could blow out to be harder than manually doing the 300 updates.
But as for the CLI, you may have found one of those little idiosyncrasies where there is no equivalent in the CLI. I have in the past taken a complete CLI config and pasted it back in, and amazingly extra bits turn up in my config that were not there before when the APIC made stuff up to fill in the gaps.
RedNectar aka Chris Welsh.
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