“The Home Owners Association of which I am a member is submitting for approval an amendment to the current Covenants which would proscribe the keeping of horses. Since horses were specifically allowed when I purchased my property and I have already invested in stalls and tack, do I have any legal recourse for an exception to the (new) restriction? Is there any relevant Georgia case law?”
Unfortunately, this is such a specific situation, and specific to Georgia law, that you really need to consult with a Georgia attorney who specializes in Georgia property law in general, and homeowners associations in particular.