please have a look at the ADL API: http://developer.amd.com/tools-and-sdks/graphics-development/display-library-adl-sdk/
ADL provides you functionality to grab an EDID and to emulate the EDID on a certain connector. Please have a loot at the functions: ADL2_Adapter_ConnectionData_Get / Set, ADL2_Adapter_EmulationMode_Get / Set. The SDK comes with a sample called EDIDSampleTool that shows how to use ADL to emulate EDIDs. This sample is a command line tool that might already provide all options you need. Unfortunately the sample is written for Windows but I believe it is not too hard to get it ported to Linux.