Do you ever ferment or age your cider with flavoring agents. Think cinnamon, cloves, or less common ingredients like hibiscus, rose hips, grains of paradise...
There's a perfectly good word for this kind of drink, namely fruit wine. And I do like fruit wines, including flavoured apple wine. Fine stuff.
But cider is fermented apple juice.
Perry is a similar product made from pear juice.
How about adding fermentable sugars to increase the potential alcohol content or back sweeten?
I don't mind sugar addition to apple juice during years when bad weather, drought, etc. have caused unsually low sugar leveles in apples. Adding more than what is naturally possible in apples leads to in my opion too high ethanol%. I prefer ethanol taste to be hidden undearth the cider flavours.
Back sweetening is ok, altough I find keeving to produce vastly superior, more complex and more fruity sweetness and flavours than just dropping in sweeteners after fermentation.
http://www.cider.org.uk/keeving.html
How do you feel about adding bottled tannins and acids as opposed to natural sources of those same things?
Tannin are really diverse and complex group of plant produced phenolic compounds. Exact chemical make up varies greatly among plant species and even between different parts of an individual plant.
All tannin additives I've seen are either from tree bark or grapes. I'm not out to outlaw their use, but I don't find these to be proper subtitutes for real apple tannins in real cider apples. I prefer my tree bark in ... umm well.. in tree bark.
Apples are so full of malic acid that its almost impossible to blend juice with too high pH. I can only see that happening if using single variety dessert apples for juice. Thats going to taste dull, with or without more acid. On the other hand, apples have so much malic acid than adding bit more doesn't really make it any less of a cider.
I know these are fairly common practices, but I wanted to get a feel for what you cider purists think about people doing this and still calling their product cider.
Free country and so forth. Do whatever you want. These were just my thoughts.