Dear GoG, why am i forced to install 2.0, why can i only download the webinstaller THAT IMMEDIATLY DOWNLOADS THE FULL INSTALLER?
WTF happened to you guys? did you change to catholic missionaries trying to force your religion upon me?
I was perfectly happy with the way it was, but because i recently upgraded my PC and changed the system drinve, i can't use the old install..

https://www.gog.com/forum/general_beta_gog_galaxy_2.0/how_to_keep_galaxy_v12_client_and_avoid_the_forced_v20_beta_update/

That's a topic which covers a fairly simply method of reverting to a pre-2.0 build of Galaxy and preventing it from automatically downgrading itself to the new client.