Unfortunately, I think the new client can only connect to official servers, however you can create a private session, and invite friends.
Yes, following the steps will lead you to guarentee if you do it correctly.
All you need to do is keep a backup of paul.dll, apply the old patch from the old patch update, put back Paul.dll, then launch the game via (Steam).
ONLY run via steam if you haven't before. I recommend running the game via steam before downgrading. Run the game until you can move your character and exit out and proceed downgrading. This will fix license issues.
if you don't care for online (private sessions), there's a mod for that, however it's something that you shouldnt worry about, unless it effects lcpdfr in a way, but as said the game must be activated first. I am unsure about pirates games.