mod for experience gain in the campaign.

Okay, let's try this:
1) You need to enable the advanced map editor.
In the game folder, find the profiles folder, and in it, the editor.cfg file.
You need the second-to-last line.
setvar map_editor_mode = 1
Change 1 to 0.
setvar map_editor_mode = 0

2) Launch the editor, create a map.

3) We need to create a new auxiliary window.
Attachment 70086

This is what the window will look like; I don't know where it will appear for you.
Attachment 70087Attachment 70088

4) Configure the window: right-click on the two bars; nothing will happen if you click anywhere else.
Attachment 70089

5) Click the "select tables" button. A window will open; in it, select AdvMapDesc.
Attachment 70090
Click OK.

6) Done! The list will contain game maps; double-click to open them.
Campaign maps are located in the Scenario folder and are simply marked with numbers, e.g., C2M3 - Campaign 2, Mission 3, Argil invades Erathia.
Attachment 70092

To remove the level cap, go to the map settings and uncheck the box.
Attachment 70091