How can I change a person's spending limit for one project in Authority Manager without affecting their other projects?

Each authority assignment is handled as a unit. An assignment is created by one pass through the grant wizard, and results in one white or gray row in an authority view. If an assignment includes more than one project (or task, or award), the same limits and conditions apply to all the projects (or tasks, or awards) in the assignment. If you need to set different limits or conditions for specific projects (or tasks, or awards), create a single assignment for each one.