void Main()
{
	var str = @"8645F8A9-DF41-482A-9C8A-3197FD77A071,0F0A911E-ABF8-444E-99C6-3849325482D4,F4EB1F14-25F7-4014-AAB7-ACFB49CA9DAD";

	var asBase64Str = GuidsToBase64(str);

	// (asBase64.Length == 64) == true;

	var backToGuids = Base64ToGuids(Convert.FromBase64String(asBase64Str));
	backToGuids.Dump();
}

static string GuidsToBase64(string guids)
{
	var splitted = guids.Split(',');
	var asBytes = splitted.Select(Guid.Parse).SelectMany(x => x.ToByteArray()).ToArray();

	return Convert.ToBase64String(asBytes);
}

static IEnumerable<Guid> Base64ToGuids(byte[] data)
{
	var numOfGuids = 3;
	var asStream = new MemoryStream(data);

	for (var i = 0; i < numOfGuids; i++)
	{
		var guidBytes = new byte[16];
		asStream.Read(guidBytes, 0, 16);

		yield return new Guid(guidBytes);
	}
}