I made a modification to the Middle Earth map called Middle Eart Fords. This removes all crossings on the Anduin, except at Osgiliath and the Old Ford. Otherwise, they used boats and rafts, which you can still build. The Anduin was a major impediment to armies, which is why Osgiliath was so crucial to Gondor. O modified the map and the program (xml file). I think I tested all the old crossings so that they don't work.
This should give Rohan a bit of a breather. Their main problem was Saruman and the Dunlendings.
if you are ONLY changing things in the xml file, THEN you can make what is called a "mod" or "variant",
which means the map can be distributed as only the xml file (ie: no other stuff, like artwork, with it)
this is because the xml file points to the original map folder, even if the xml file is itself in a different place
(for examples on how to do this, download any of the variants in the download list, like NWO_variants, etc.)
if you are going to change territory names, etc, then this will require the map be downloaded with new artwork, etc.
Whenever possible, I prefer people to use the first method for their mods/variants
this is because a 100kb xml file is very easy to distribute and keep up to date, while having multiple copies of all the artwork for a map is much more difficult