There are only 10^80 atoms of matter in our entire universe. If you feel that you can mathematically demonstrate that there are 10^280 viable variations of a genome with certainty, then please post it as it would change Watson's mathematical conclusion for this thread.
Without that math, however, you're just whisteling Dixie.
I'll try. Let's stick to coding sections of the genome. IIRC current estimates are that there are ~30K genes. Let's say the average gene codes directly for a 100 amino acid protein (I'm sure this is conservative). That gives 3*10^6 codons.
As you know, there is significant redundancy in DNA coding. Every codon can code 64 values but there are only 20 amino acids. Let's go wth the average and say that every codon can have three variations.
Varying all the codons independently gives 3^(3*10^6) functionally equivalent (hence viable) humane genome variants. That's ~10^954242.