If I am not mistaken, to do your own annuals on an Experimental category plane, the owner had to do over 50% (or maybe more) of the building of the aircraft? If not, then the plane is treated like any other plane?
That's pretty much true, the so-called "51%" rule. There are some important details, but the spirit of the rule is correct.
However, that's only true when you build the airplane from the ground up. Disassembling and reassembling a certified aircraft does not make it Experimental, no matter how many parts you replace.
Also, there are various flavors of Experimental. Home-built experimentals are the least restrictive. Modifying a certified airframe places it in one of several other types of Experimental classes (categories?), depending upon the nature and extent of the changes. But those types of Experimentals are very restricted in the allowable flight regimes.
There was one case of a Helio Courier that had so many major modifications (new engine, landing gear, wings, etc.) that the FAA considered it a home-built. But I don't believe this particular Cessna 150 would fall under the same class. Clipping the wings is one thing - building a new set of wings (as was done on the Helio) is quite another.
