Many AVs can’t deal with infected restore points and that is why the general advice was to disable system restore before trying to deal with an infected file in a system folder.
avast can generally deal with viruses/malware in the system folders without system restore creating a restore point (which would be a copy of the infected file). So there really shouldn’t be any need to disable system restore.
A worst case scenario would be that avast would subsequently detect the file in the infected restore point and you can choose to move it to the chest also.
In the event avast can’t deal with an infected file whilst windows is running then avast as another weapon in its arsenal the boot-time scan (unique to avast). Since the boot-time scan is dome before windows has fully started system restore isn’t an issue and neither are infected restore points.
So with avast this isn’t really necessary.
Like everything there are exceptions to every rule, but we know nothing of what it is that you are dealing with (the virus name, file name and its location, etc.), so we are unable to give detailed advice.