I just picked up a McCarty 594 SE and I think it came with 10's. I am planning to put 9's on it. It sounds like since I an going down, it shouldn't be an issue. I was concerned about that.Going down a gauge is less likely to cause any issues with the way the nut was cut as it's only slightly 'smaller' in diameter, so not going to 'catch' or increase the friction at the nut to cause Tuning issues, if you were going up in gauges, you may need to widen the slots a 'bit' to prevent increased friction affecting tuning, but a gauge either way is 'generally' OK
Thanks for the info.