The way the AI shuffles workers is not something that the modkit cna touch. There's the list of open jobs that you set up in your game as you grow your town, and the AI decides who does what, based on global pathing optimisation.
There's no way to automatically have one type of jobs switched to another. There is no way to tell the AI that a building will not work in certain seasons. The "farming" job that tells people to go start planting at the start of spring is not something that can be tweaked to be applied to other stuff.

As a side note, any assigned worker that cannot do his regular job (farmer in winter, blacksmith when you have no steel, woodcutter when you've reached the firewood limit, etc etc) will act as a labourer until he can resume his regular work.