First, I'm no expert so sorry if I get anything confused but I tried to research as much as could before asking this.
So while it is pretty much accepted that photons are massless (Despite this question, I do believe this to be true), we also know that it is possible it could just have a very very very tiny mass. I think $10^{-54}~\rm kg$ is currently the maximum possible limit it could have.
So my question are, if the photon does end up having mass, then what effect would that have on the value of $c$? Is it possible the new $c$ could be infinite or almost infinite? Or is more likely its just slightly faster than a photon.
Second, what implications would this have on the expansion of the universe? We know that universe is expanding faster than light can keep up with it due to what we know of space-time. Would there be any kind of possible correlation between this new $c$ and that expansion?
Edit: And to clarify, when I refer to the new $c$, I mean the speed of a possible massless particle in the case that photons have mass. Not the speed of light in a vacuum.