Parts tolerance simulations in ltspice
Monte Carlo analysis and worst-case is usually the way this is done, exactly as the linked article describes.  For Monte-Carlo you don't have to change your components by hand, just run the Monte Carlo sims and the simulator will automatically change the components based on your Tolerance field. You have to run enough cases to get a statistically significant result, and you can calculate how many runs you need for a given confidence.  Worst-case requires a little more work and knowledge of how the circuit works, but the linked article explains that as well.