I'm under the impression that if I purchase an experimental gyro if I make a significant alteration I might have to go back to phase 1. But I could repair. So if I change the prerotator or replaced the engine I could still be legal but I might have to go back to phase 1. Even if I'm not the original builder. Is that correct. ?
Mark Givans built The Predator.
When I changed from a Lycoming O-290 to a Lycoming IO-320, changed to a different propeller and changed rotor blades I filed major change paperwork and visited the Flight Standards district Office (FSDO). They defined the new phase one.
Then two gentlemen from the FSDO came out and after inspecting her with the major changes pronounced her airworthy.
I was to fly phase one for 25 hours inside a circle around Santa Maria.
I found 25 hours was not enough to do phase one.
Things may have changed and each FSDO (they may not be still called that anymore) is unique and may have different procedures.
In my opinion the best thing to do is to call your local FSDO, tell them what you would like to do and let them decide if a new phase one is required and the procedure for that.
The Van Nuys FSDO likes to know when an experimental aircraft comes into their territory.