I can’t remember how long ago or the context where this came up, but there’s a neat Fate trick I stumbled upon a bit ago. If you’re a Fate junkie, I recommend you first take a look at Lenny’s post on the Fate RPG site about trappings & how they relate to skills and stunts.
With me? Good. So, mix the following together: stunts that allow for trappings to attach to another skill (a.k.a. skill substitution) & the idea of invocation for effect (where you use an aspect & fate point to justify something about the world or current situation). You get…
Invoke for Temporary Skill Substitution
If you want to substitute using one skill for a given trapping of another, and can justify how one of your aspects allows you to pull off that substitution, you may pay a fate point to substitute that skill for the rest of the scene.
Example: Sally Slick’s fighting Doctor Methuselah’s Steel Vanguard — automations larger than a man, able to withstand gunfire and are damned cunning…as though a human mind were housed inside those metal monstrosities! She has the aspect “Monkeywrench,” so she justifies that her Engineering skill should allow for the “I can attack you” trapping. She pays a fate point, and for the rest of the fight, her wrench is a weapon those chrome fiends will come to rue!
Interesting-to-me aside: the combat functions in Fate are implicit trappings, in that some skills have the privilege to cause stress and the effects that causing stress has.
The potential for abuse?
I’m not sure if this has any more potential for abuse than the +2/reroll that regular invocations have. The thing about the Fate point economy is that you have a built-in mitigation for abuse. You want people to spend Fate points. That creates the desire for compels, the engine that makes a Fate game work. But I could be wrong there. More play would show the answer.
Of course, if someone keeps doing the same substitution over and over, they might just want to take that as a stunt and save themselves from needing a Fate point.
 $20 says it was a conversation with Lenny Balsera. We have a habit of brainstorming a lot about Fate over cocktails.
 Of course, in pulp I allow anything to be a combat skill, so with respect to my games (and the Spirit of the Century games GMed by others that I’ve played) this is a moot example. Still, I wanted to dust off the iconic Spirit characters. It was either that or bring in Dick Awesome. :)