well, YES they can

s223 a86 does NOTHING to stop the FAA from regulating toy airplanes,
its very core is that it fully expect there to be FAA regulations on toy airplanes.

What it does is say some groups are allowed out of those regulations,
but it does nothing to protect those groups existence at the leisure of the FAA in the first place.

We have been over this ad nauseum:
The FAA could ban Turbine in models.
The AMA will then attempt to claim a senate provided CBO exemption from that regulation,
but the FAA can simply say they accept no CBO Standards that allow Turbines
... ergo AMA is NOT 'senate cbo exempted' from the regulation