Found a web page on Photon Absorption. There are three main processes of same.
µPE ~ Z5Where µ is an absorption coefficient.
µPP ~ Z2
µC ~ Z
Of those three, only the low-weighted Compton Effect seems to be momentum dependent. The other two absorb all the photon's energy and thus from what I can tell would not be so fragile in a Setterfieldian world.
A web page that ties at least some of the concepts involved together is here.
So cancel some of the alarm. ASSUMING I AT LAST HAVE THIS RIGHT (but I'm no physicist), we have the following.
Chlorophyll still works on Earth. So do eyes. However, we also have restored another factor of 11 million that the Sun has to swell, since opaque things then are indeed almost as opaque as now and they are getting all the photon energy, not just that tiny momentum. I hope it's clear by now that I don't think opacity does good things when it "works."
It also means all of the energy and not just the momentum of a given photon is available to knock gas particles across space. That means radiation pressure on free-space objects should have worked 11 million squared times better than now in the first days and in proportion with c squared down the decay curve. Given the alleged decay of c just within historical times, we should perhaps see things relating to dust clouds happening faster in the 170,000 light-years distant Magellanic Clouds than in closer objects like this one. The slowed-frame effect which has been invoked repeatedly on this thread is still there but shouldn't cancel.
Astronomers should be arguing over the odd "speed-up" effect as you look back across time in the dissipation of dust and gas around stars. I am not aware of such a discussion. This would seem to be a failed prediction.
I'm not even going to ask why some stars appear first-generation and some stars appear second or third-generation in our universe if they were all made at the same time.
The full photon energy increase of 10^7 does not resolve into increased volume of 10^7. Opacity doesn't cause volume increase as the only resolution of the equilibrium. (My earlier example was to illustrate that decreased density would manifest in increased opacity, but as h decreases, density decreases with the square, without changing the volume.) Rather, the decreased density causes both the increased opacity and the increased photon output which registers as an energy increase. You have correctly noted that the mechanisms of absorbing this energy include photoelectric effect and pair production (which appear to be more likely) as well as scattering.
It also means all of the energy and not just the momentum of a given photon is available to knock gas particles across space. That means radiation pressure on free-space objects should have worked 11 million squared times better than now in the first days and in proportion with c squared down the decay curve.
I'm sorry, with the variations in your explanations I'm not sure why this follows. The photon energy increases by 11 million times, not its square; and part of the increase can resolve into increased radiation pressure in equilibrium, while much of it resolves into heat.
If energy output increases only with c, not c^2, I think it will in fact cancel with the slowed-frame effect, because the increased output is similar to the radiometric decay which started this topic. Observations of it would be consistent with both assumptions (constant or variable atomic time). Observational evidence for VSL comes from elsewhere, of which I've provided many examples that I haven't seen answers on. Dark matter is a biggie.