Since a couple of people were wondering how to do this themselves, I thought I would share how I managed to do this.
Only one program is needed to apply the modifications: Yogda. If you don't have it, google Yogda 1.0.564.
Once you have yogda you need the game client. To download the current client you'll need to go to
'http://www.realmofthemadgod.com/AssembleeGameClient[NUMBERS HERE].swf" and use your browser's save as feature.
The numbers can be found by visiting the rotmg homepage and looking at the source.
Now we have everything we need, lets make the changes to the client.
Load up yogda and open the client file. Once there, navigate to AVM2 Bytecode - WebMain (frame1) - Strings. Right click strings and click on find to search for "rotmgtesting.appspo*****m". Once found, double click on it to change it to "realmofthemadgod.appspo*****m".
That change will allow us to connect to the non test servers.
Next we get rid of the black loading screen. Navigate to AVM2 Bytecode - WebMain (frame1) - Classes - com.company.assembleegameclient.game:GameSprite super(flash.display:Sprite).
Now we need to look for a private function in GameSprite that has the string "<p align="center">Loading...</p>" in it. It won't neccesarly be _-WI() like it shows in the pic.
Once found, scroll to the top of that function to the very first line, it should something like "0 27 pushfalse" (doesn't really matter what it says). Double click that and change the instruction to "returnvoid".
Thats it. Save the file and play rotmg.
A side note: Some of you will notice that it still says Testing v123.4.4 or whatever and the connection messages show Testing in it. That's purely cosmetic. To get rid of them, one needs to get rid of the Testing strings. I'll leave that for you guys to figure out.