I just wanted to make it easier ;) I can easily write the path manually, but someone else might make a lot of mistakes. In general, you can try adding them through a mod to the editor, but for now, I'm too lazy to do that and need to use it like this for now.
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In your mod, some files are missing for correctly entering paths, and the paths you specified are incorrect. They should look like this:
AdvMapHeroShared:MapObjects\Inferno\Nymus.(AdvMapHeroShared)
So, there's one mistake in this line - and the editor won't save it (+ the file must exist, which is irrelevant).