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 and create a map.
3) We need to create a new auxiliary window.
This window will look like this; I don't know where it will appear for you.
4) Configure the window; you need to right-click on the two bars; nothing will happen in other places.
5) Click the "select tables" button; then, a window will open. In it, select AdvMapDesc.
Click OK.
6) Done; the list will contain the game maps. Double-click to open them.
The Campaign maps are located in the Scenario folder and are marked with numbers, for example, C2M3 - Campaign 2, Mission 3, where Argil invades Irollan.
To remove the level cap, go to the map settings and uncheck the box.