In my opinion...
<snip>The word appreciable is open for interpretation....<snip>
That has ALWAYS been the problem. Interpretation could vary widely on what is "appreciable."
I might suggest that if you contact the FSDO, you get an answer in writing from them. Think about it. You contact the FSDO on the phone about changing the prop, he says it is a minor change so no Phase 1 needed, no revised For 8130-6 needed. You hang up the phone and head for the hangar.
You change the prop, but then have an accident. You make a claim and your insurance company starts looking at the logs and sees that you made a prop change. They get an expert that says that your prop change is a major change, and you didn't contact the FSDO about a test area, and didn't go back into Phase 1, and didn't submit an 8130-6. You broke the rules and now they won't pay.
At least if you have something in writing from the FSDO stating that in his opinion the change was not "appreciable", and therefore you didn't need Phase 1 and the 8130-6, you might have a chance.
I just spent the money to have my OL updated to the current version. The version on the plane I purchased stated that a major change was changing the make and model of a prop, and that Phase 1 and an 8130-6 was required. The current OL say that a major change is going from FP to CS or back. I wanted to be able to change the prop pitch and not have to worry about the 8130-6. To be on the safe side (legally) I probably would still contact the FSDO for a test area and go back into Phase 1 for the 5 hours.
Good Luck and let us know what the FSDO says...