Years ago, customizers (or folks who thought of themselves as customizers) would spread falsehoods to confuse and frustrate their competition and to build up their reputation.
Myths long-since debunked are still spreading like they are bits of secret knowledge that someone doesn't want you to know.
Customizing the diatonic harmonica takes skill, patience, high standards and common sense. There are no real shortcuts. Putting in the time and effort needed to make the slots perfect before doing reed work *is* the shortcut.