What odd advice.
If a manual player's pass percentage is below par or expectation i'd simply recommend him to be more careful in his passing, and, depending on the particular reason behind his (un)forced errors, to become more mindul as to prevent giving the ball away too easily.
Same goes with shots.
If you miss target too often, simply review the situations in which you have shot too hastily, or whenever you have released a shot that had a small chance of actually being scored.
To bypass the finetunement of the player's own set of skills and behaviour on the ball, by abusing sliders in order to narrow down the repercussions of your own mistakes, is quite worrying to me, and forms exactly that sort of qualm i've been having with a large chunk of motivation that has driven many players in the past, and to this day, to mess with sliders way too early on, before even having put in a decent amount of hours in training sessions, cause that's what ''professionals'' are meant to do, right?
Train to become better, not instantly grab the crutches!