I've mentioned that as "growth factor" if you cared to read my post. Growth factor is fixed, the only way to change that is to replace the player which is a moot point, that's why I don't talk about it. Train factor on the other hand will change depend on your commands on the player.
And no, you can't detect a fast trainer at the higher levels unless you train him, as player value appears to be capped at 106m.