I am using Worldbuilder to change the map although i don't put them back into '____edain_maps.big'. I put them in the following folder :
C:\Users\[USERNAME]\AppData\Roaming\Meine Der Herr der Ringe™, Aufstieg des Hexenkönigs™-Dateien\Maps\[MAPNAME]
(The "Meine Der Herr der Ringe™, Aufstieg des Hexenkönigs™" might have the english name in your case i guess.)
For example the Folder
'C:\Users\MyUserName\AppData\Roaming\Meine Der Herr der Ringe™, Aufstieg des Hexenkönigs™-Dateien\Maps\map wor black gate' contains the following files :
- map wor black gate.map
- map wor black gate.tga
- profile-high.csv
Then the map appears ingame for me (i normally dont change the name so that i have two maps with the same name in the end). This way i change the zoom and command points.
Also might be a good idea to move big files to another place and edit them there. Just move them back when you're done.