For patches that don't change any unit stats, you can use a hex editor to change the version identifier at the very start of the .rec file to make it work again.
For patches that do change unit stats, nothing can be done short of having a version of coh2 locked in that one by disabling patching in Steam (will it even allow you to run it though? I don't know).
For the patch that just got applied, no stat changes were made so the replays will work fine. Open up the rec file in a hex editor (HxD is very simple and requires no installation http://mh-nexus.de/en/hxd/ ), and change the start of the file from 00 00 7A 36 to 00 00 66 37.
Thank You. I did it, and it works.
So i can launch the replay it is working fine, but i see "sync error detection" in the middle.
Do you know why? What is Your opinion, how can i hide it?
Thank Your answer.