In article ,
stargene writes:

rho(M@z)= rho(Mz=0)x(1+z)^3, for the universe at any value of z.
Eg: At a z = 4, the mass density of the universe at that point in its
expansion (at about 13.8 Gly (z=0) - 12.77 Gly (z=4) = ~1.03 Gly),
would be roughly 5^3 or 125 times its current mass density.

Not "roughly"; pretty much exactly. Of course, this is the average
density.

Would any of the deep galactic survey programs, like the Hubble
Ultra-Deep Field, actually be capable of detecting such an increase
in both the average mass density, and perhaps even the number-
density of galaxies, possibly correlating with such a higher mass
density?

[[Mod. note -- I doubt it. It's already rather difficult to measure
the mean mass density of the local universe (z=0),

The radiation density goes like (1+z)^4 (photons are diluted by (1+z)^3
like non-relativistic particles, and additionally they are redshifted by
(1+z)). This CAN be detected.