Yes you have: that recprocity applies between all frames and not just inertial frames.I haven't inserted any rule to STR.
When analysing the ageing rate of the mothership observer as seen by one of the travelling twins, you keep imposing that what I call $$T_a$$ and $$T_a'$$ in post #75 are the same (or at least that the former is "negligible"). This is your own rule, not relativity's. Special relativity doesn't directly tell you what $$T_a$$ is.
There isn't a single Lorentz transformation that relates the travelling twin's and mothership observer's rest frames for the duration of the trip. If you use two transformations for the two inertial segments (before and after the acceleration), fine, but you can't simply assume whatever you like about what the accelerating twin sees as he switches from one inertial rest frame to another, then claim you've disproved a theory that doesn't make this assumption.
As far as General Relativity is concerned, your view is quite explicitly contradicted:
Gravitational time dilation is manifested in accelerated frames of reference or, by virtue of the equivalence principle, in the gravitational field of massive objects. In more simple terms, clocks which are far from massive bodies (or at higher gravitational potentials) run faster, and clocks close to massive bodies (or at lower gravitational potentials) run slower.
If you're in an accelerating reference frame, anything you are accelerating toward is at a higher gravitational potential than you.