It'd have to be much more distributed in its ability to react, like octopuses arms being semi autonomous. They'll continue to pass objects towards the body even after being severed.

Or consider the humongous fungus: https://en.m.wikipedia.org/wiki/Armillaria_ostoyae

Sure, but it's not clear in this case whether say the human species should also count as a single "organism". We don't understand very much about the octopus, which is a healthy reminder of why I shouldn't even speculate about alien life which would almost unavoidably be much stranger than an octopus - but we feel comfortable asserting that the "semi autonomous" limbs of the octopus are not distinct in the way that say, my friends Chris and Caroline are distinct people. So if this galaxy sized organism consisted of smaller units with similarly distinct properties, I think we'd say that's not a galaxy sized organism that's a culture of individuals.

Good point. Of course this presumes that we understand the physics at that scale, and that there's nothing akin to a quantum tunneled nervous system, etc.

think it's relative upward and downward in scale. an entity at universe scale might be moving similar speed to us in our 3d space

No, I assure you that the constant is not concerned with scale, we're easily able to check that. A bigger device does not make this constant larger or smaller, you may be able to get more accurate results but that scale is unaltered.