EPM base file edit for Polycom phones

I am making custom edits to base files using the Commercial EndPoint Manager for Polycom 501 phones (I know they are not supported). But it gives me the following files to edit:

MAC.cfg   MAC-Features.cfg   Ext.cfg   SIP-Interop.cfg

and there is no documentation on which files this translates to once the base files are generated.

In my /tftpboot/ I see a "legacy-sip.cfg" that apparently holds global configuration for all phones. Which file above edits this file?

I also see a "MAC address-extension.cfg" that seems to have specifics, but what file above edits this?

It seems like Ext.cfg is the only file that has options in it already.

Help!