Not really. They'd still get the benefits of being a Spark for things they aren't trained in it. It's just that they aren't trained in it, so they don't get the benefit of skill ranks and the like. A baker who happens to be a Spark will still benefit from the Spark if they happen to attempt to repair a Clank (mechanical automatons, basically robots, but working off technologies existing in Girl Genius like clockwork), but they probably won't be able to pull off anything truly spectacular.
I am thinking of a new mech, built by Nergal Heavy Industries from Mobile Battleship Nadesico. Named the "Gospel" it is based off the frame of the experimental X-Aestivalis and incorporates knowledge gained by studying the "Gekiganger-type" super robots used by the Jovians. It's primary weapon is it's field lancer, which is designed to penetrate barriers, based on the similar weapon used on the Aestivalis. It can also use the Gravity Blast like the X-Aestivalis, but has to deploy the weapon before firing. It is also protected by a barrier of it's own - the distortion field. Rumor has it that this model is designed as a rival to the Evangelions, noting the name of the unit and the barrier-penetrating abilities.