Besides all of the points (which of course are totally right on) already mentioned by Vic and Mel, is the point to keep in mind that W & B change is not the only factor.
The FAA considers any change that could effect the W & B, the reliability (this is the one that can be the most fuzzy to define IMHO), or performance/handling, to be a major change.
The actual text in FAR 21.93 (which E-AB operating limitations refer us too for the definition of a major change) is......
A ??minor change?? is one that has no appreciable
effect on the weight, balance,
structural strength, reliability, operational
characteristics, or other characteristics
affecting the airworthiness
of the product. All other changes are
??major changes?? (except as provided in
paragraph (b) of this section).
W & B - that is an easy one.
Structural strength - A bit more challenging, because few of us are engineers
Operational Characteristics (Performance/handling) - This one can be a bit more complicated...
So, you changed from one wood prop to one made by a different manufacturer and the pitch is only one inch courser than the one you previously had.... That doesn't mean a thing until you test it and prove that the climb performance is acceptable.... Many of the prop makers measure their pitch values in different ways. The pitch value from one does not necessarily match up to the pitch value from another.
Reliability - This one can be the most difficult of all because it is the one that has the widest latitude for personal opinion.
My opinion (and that of at least a couple FAA people I have worked with over the years) is that any configuration change to something related to an important flight function of the airplane (engine, flight controls, etc) is a major change.
So, if you switch from regular mags to P-mags - Major change.
Carb. to fuel injection - Major change
Even just installing a different induction airbox that you designed would be a major change because it could adversely influence engine performance / power output.
The thing to keep in mind is that none of these or any other changes will automatically effect W & B, Performance, and/or Reliability, but until that is proven (via some level of flight testing) it is unknown.
Regardless of whether you agree or disagree with the above, we still always have FAR 91.407 which reads......
?91.407 Operation after maintenance, preventive maintenance, rebuilding, or alteration.
(a) No person may operate any aircraft that has undergone maintenance, preventive maintenance, rebuilding, or alteration unless?
(1) It has been approved for return to service by a person authorized under ?43.7 of this chapter; and
(2) The maintenance record entry required by ?43.9 or ?43.11, as applicable, of this chapter has been made.
(b) No person may carry any person (other than crewmembers) in an aircraft that has been maintained, rebuilt, or altered in a manner that may have appreciably changed its flight characteristics or substantially affected its operation in flight until an appropriately rated pilot with at least a private pilot certificate flies the aircraft, makes an operational check of the maintenance performed or alteration made, and logs the flight in the aircraft records.
(c) The aircraft does not have to be flown as required by paragraph (b) of this section if, prior to flight, ground tests, inspection, or both show conclusively that the maintenance, preventive maintenance, rebuilding, or alteration has not appreciably changed the flight characteristics or substantially affected the flight operation of the aircraft.