If you want to change ini-files, you should always first extract them, edit the file and then add it to your ini again. If you modify it directly, there might occur some problems and the game won´t change anything at all. (Had to learn this the hard way myself
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You have to change two entries, to enable 6 players. First of course, set MaxPlayers to 6 and two lines below, delete all Regions listed in "DisallowStartInRegions"
But remember, to not change the original files. Just create a new big-file, name it _wotr or something like that (" _ "is important) and add the eddited files as "data\ini\campaigns\scenarios\..." If you copy this big to your RotWk folder, it should work fine.