skill window
 

As far as i could see in the "can't be done" list, the skill window doesn't seem to be mentioned.

Would it be possible to mod the skill window so related skills are listed next to each other?
Like all the tradeskill-skill's in a group.
Havesting skills in a group.
Combat skills.
Spell skills.
Skills that determine what equipment you can use.

Sorting things in Alfa or skill size doesn't seem enough.

No, that can not be edited.

Barring some SOE hard-coded thing, data lists can only be alpha and revers alpha sorted based on the available columns. Since there isn't a column for skill categories, we can't sort on that.