So, on the permanency of workings. The corebook makes some pretty strong statements about their durability. Here's a couple big exceptions
1. The working is, by its nature, temporary. If you brew a potion that turns someone into a cat-headed ogre for three days, it's only going to last for three days.
2. Sorcerous weirdness says so. When the player and the Storyteller work out the mechanics of the working based on Finesse, "when is this going to end?" and "is it gonna break down and get weird down the road?" are valid considerations to discuss. Botches can also add complications that take on this form.
3. The sorcerer builds an end-condition into the working. This can potentially overlap with both of the above categories. Why would you do this? Because once the working expires it becomes narratively irrelevant, and you get the XP you invested in it back. Frugal!