I haven't seen a single guide about this and from what I've seen, not many people know how to do this. So I figured I'd make a quick guide about it!
If this isn't your server, you can go ahead and skip to step 2!
Tools Required:
1 - SQL Server Management (HeidiSQL, Navicat, etc..) - This is only required for Step 1!
2 - DBC Editing Tool (MyDbcEditor, Taliis, etc..)
3 - MPQEditor
4 - World of Warcraft (duh)
STEP 1 (Server-Side): Adjust the level requirements in the database
Note: This was made on a Trinity-Core server, so yours may be slightly different!
First, launch your SQL Server Management Tool (I will be using HeidiSQL) and log in.
Next, select the World database and then scroll down to battleground_template.
Click on Data to show what's inside that table and go to the MaxLvl column (5th) and change all the values to 255
That's it for the server-side!
Your server should now be able to let players queue for battlegrounds at level 255, however
if you only did this step, you will have to queue from an npc as the BG pane won't be available
STEP 2 (Client-Side):
Now that your server allows you to queue, you need to let the client know about what's going on!
First, if you haven't, you need to extract "PvpDifficulty.dbc" from "patch-enUS-2.MPQ" located in WorldofWarcraft\Data\enUS\
Next, once you have the dbc file, open up PvpDifficulty.dbc
Let me explain how this one works real quick first!
This file basically holds the information about the level brackets for battleground (Warsong Gulch 10-19, 20-29, etc..)
So here we don't want to change all the values, we just want to change the last bracket of each instance so that it includes level 255 players.
So now once it's opened, change the last value of each MapID in the 5th column to 255
I'll make this easy for you, the rows you need to change are: 4, 12, 19, 35, 51, 54, 70, 73, 89, 105 and 108
Once this is done, save it (Ctrl-S does not work for MyDbcEditor, so just click on File and then Save)
Note: You probably don't need to change ALL of them to 255, but I like to do it just in case.
If you only want to change the values for BG's and don't care about arenas, the values from the second row of PvpDifficulty.dbc corresponds to the second row of BattlemasterList.dbc
That's it! once you did all that, create a new MPQ file with MPQEditor, then create a folder named "DBFilesClient" and put the dbc file Inside that folder. Once the patch is ready, insert it inside your Data folder.
The next time you log in, the Honor Pane should be available!