I think the laws might have changed slightly (I'm talking less than 0.01% since the very early universe). It seems you're aware that the laws could have been different right after the big bang, there's also serious work being done since then by real scientists.
However, even if these ideas become conclusive and gain the scientific consensus, it won't do much for the creationist position as the changes are too small to effect things like radiometric dating, age of the universe, or using light from stars to show a minimum age in any meaningful way (it's like saying the universe is 99.9 years old instead of 100 years old).
Don't know why the laws changed (assuming that they did), but there is evidence that they have based on analysis of quasars (and comparing their spectra with spectra of closer/earlier stellar objects). I can't post links yet (not enough posts yet) but for references look up the work of John Webb and Victor Flambaum on quasars and variable speed of light hypotheses in cosmology.