There are two if you have patch installed (main 10,5 GB vs patch 2 MB). They are hardcoded in executable, so you can't add another one.
But adding files to second archive may not work.
FF XII works by using ID numbers to take files (for some of them, if not for all) and if you will add file to patch vbf, then they will be probably ignored (it will depend on engine if files from patch vbf are hardcoded to executable - I didn't check). I don't know if dds.phyre files are working with this.
For example with repacking patch archive you can't apply translation mod. I've already tested and files were ignored. Only by repacking files from original vbf translation was working.
ffgriever added experimental function for packing archive, but it can mess with files that are already in patch because of IDs (there are two of them).
tl;dr
It's a big chance that repacking FFXII_TZA_PATCH.vbf do nothing. Repacking FFXII_TZA.vbf is probably only solution before SaltyNX will be released.