I am mimicking a poorly-tuned piano by creating two identical piano tracks and de-tuning one of them by some fraction of a tone and giving it about half volume. Works good enough. However, it's a pain because every time I need to change something in that part I need to re-copy the original track's clips to the de-tuned track. Isn't there some way where I can have the de-tuned track automatically slaved to the main track without having to physically copy the clips every time?

Link the clips and use pitch wheel automation to detune one of the tracks assuming the key slider setting is too coarse an adjustment.

Thanks. Simple as that. It was linked clips I'd forgotten about. And yes, I'm using the pitch wheel to de-tune.