Is a restore from a backup a possibility?
You can try reinstalling using an older GSX installer with the network connection disabled, so the updater won't run at the end.
But it must be an installer that you downloaded before we posted the 4.1-only update (March 30th) because if you downloaded the GSX full installer after that date, even the files contained in it are 4.1-only so, disabling the network to prevent getting the latest ones won't work.
We don't have old installers around anymore, and we don't support doing this, because it's too much support effort for us supporting users, if we are not even sure they are using the latest version. Of everything, both GSX AND the sim.
I'm sorry, but you really have to vote with your wallet here, and support developers that constantly update and support all the latest versions of any supported sim, rather than those "thinking about it".