That may have been true with older heads...mostly solid re-shapenable heads.
Todays heads (Including Muzzy) are held to a tighter tolerance than you can shoot. Changing blades should NOT effect your flight, and in my experiance, the Muzzy practice blades work VERY well.
I NEVER resharpen replaceable blades...doesn' t mean you CAN' T, just that I don' t (I WILL touch them up SLIGHTLY though when new) Thin blades get nicks in them, and you end up taking (IMHO) too much matterial off when re-sharpening them...NOW you lost your tight tolerance.
Simply put, tune your heads with the practice blades...or, if you must, use hunting blades to tune your arrows/bow. Then just put in some fresh blades for hunting.