In your installation folder, go to the WTF map, where you will find the 'Config.wtf' file.
Open it with Notepad or any other text editor.
Make sure the >> TOP << 2 lines are:
Code:
set realmlist logon.warmane.com
set patchlist logon.warmane.com
Remove any other mentions of realm / patchlist down the list.
This will let you login normally. But you will still (very) sometimes get a disconnect when playing. This is usually caused by having Battle.net running, from any other Blizzard game (like Hearthstone) or Retail WoW. I do not recommend messing around with that. The disconnect is very seldom.