One of the design criteria for AtomBIOS was the ability for the driver to over-ride any table with a newer version if required. We have been using AtomBIOS for the Windows drivers for a few years now and have never had to patch a table, but the mechanism is there.
Luckily the hardware is quite resilient, and i'm sure the windows/fglrx driver are full of workarounds like this: http://gitweb.freedesktop.org/?p=xor...t;h=10e7636c02
Actually, that's not the case with AtomBIOS. We don't restrict you to specific modes. There is a traditional VBE / BIOS layer running on top of AtomBIOS which does have a fixed mode table, but that only affects VBE calls.