To answer part of your question, Greeks continued mixing their wine well past antiquity and certainly into the Byzantine period. And a fairly easy way to show this is in the 10th century account of Liutprand of Cremona during his visit to Constantinople. Liutprand was the Bishop of Cremona and and led two envoys on behalf of the Italian King Berengar II and Holy Roman Emperor Otto I. The second trip contains the passage of interest, in which Liutprand, who had been poorly received by the Byzantine Emperor Nikephoros II, chastizes the Greeks for their customs and in particular, cuisine. I'll paste an excerpt of Liutprand's report:

To add to our calamity the Greek wine, on account of being mixed with pitch, resin, and plaster was to us undrinkable. The house itself was without water, nor could we even for money buy water to still our thirst.

So we do see that wine was still being mixed many years after what is considered Classical Greece. On another note, the Byzantines continued some other ancient culinary practices as well. In this same report we find a reference to the famous fish sauce Garum, which Liutprand, of course, finds disgusting.

I sat in the fifteenth place from him, and without a tablecloth. Not only did no one of my suite sit at table, but not one of them saw even the house in which I was a guest. During which disgusting and foul meal, which was washed down with oil after the "manner of drunkards, and moistened also with a certain and other exceedingly bad fish liquor

While we can note how the Byzantines kept the use of mixed wine and Garum, it's interesting that Liutprand's comments indicate that these two practices had become much more uncommon fror the Western European palate.

Here's an online translation of Liutprand's 968 account if your interested. It's a very colorful telling of his visit and a fun one to read.