I suppose it shouldn't be a problem to change the map to your liking.
Whether the official map then adopts the changes or whether you have to publish your "own" map, so to speak, would have to be clarified with higher-ranking people.
If you are comfortable with the BattleForge MapEditor and the scripts, you can start without further problems. Out of respect and copyright reasons I would recommend to note that the original map is from XYZ and that you have made changes.
If you have any difficulties with the MapEditor or scripting, feel free to drop by the Discord mentioned by Mynodu