It should be enough when the marker has changed only and the private /public key pair of the SLIC haven't changed. Dannyres mentioned that the bios corrects the checksum of SLIC found at offset 9 automatically. (It's the z before the OEMID). The SLP2.1 SLIC we have got now has got the same private/public key pair and to exchange the marker data only should work, since the public key data are still the same. Not sure if it still works if the SLP2.1 marker will be another one with another OEMTableID. And I'm not sure if it will work when the public / private key pair have changed at SLIC and you need to replace both, the public key data and marker data. If the bios reads the OEMID and OEMTableID from the marker itself and corrects them as well it will work also. Every marker contains the OEMID and TableID right before the WINDOWS string, so if the bios reads them from there, and corrects them, it will work as well. I'll play with this and try to find a way to use Lzma. Since this is great news, I'll make it sticky.