lol, I'll make a reply to this thread 4 years after the last post then !
1) is this mod still useful ? Well there is a picture of the result of this mod in the 2nd post of this thread, on the 1st page. It's about the phantom ability of the rune mages. You have access to them when you reach the 2nd part of the game, reaching greenswort without any army (and I find it's unfair to have to give up the vikings at this point and it's like starting another crossworlds here, but easier, anyway it's not the subject). So in the original game without the mod in the description of this ability you have something like "this unit dies until it dies" !!! See the picture for the result with the mod, in short yeah clearly it's still useful ! That was the main drawback of warriors of the north, this forum was abandonned and everythinhg here was ignored.
2) to install the mod, the file downloadable in the 1st post gives a "ZechLang Mod.kfs" file which is actually a rar file. Well for me mods are recognized only when they are zip files ! So you need to extract the files from this in a directory and then zip them to a file with this same name, then place it in session\addon.
Thanks for the work anyway to the original author, it's a pity there was not more development around this game, with such an amount of lua inside it's almost an open source game !