[Mathias]

Skills in Shadowrun are a two part system - the skills themselves, and their dicepool helpers.

On the Dicepool Helper tab in the editor, try making a copy of the Assault Rifles item - you'll see that it is linked to the automatics skill, and then to the assault rifles and battle rifles categories of weapons.

So, what you can do is to find all the dicepool helpers for automatics, and replace them with copies that use longarms instead. That way, the longarms skills will now be linked to those weapon categories.

Then, use the *Hidden tab to get rid of automatics, and you won't even have to touch the longarms skill itself.