The most interesting thing I learnt in researching this is that newspapers don't do a very good job of proofreading these days. When I searched for retune on News Limited's Australian website, 6 of the first 10 results were obviously meant to be return - e.g. "life retuned to some degree of normality". And Rupert Murdoch wants us to pay to read this stuff online?
That kind of result - where a search retunes returns more typos than actual uses of the word - usually means that the word is reasonably uncommon. And where the word was intentionally used, on various newspaper sites, it was often in specialist articles - about cars and electronic systems, for example.
It's probably a border-line case, but in such cases, I lean towards a rare classification, so I'm inclined to leave things as they are, mkenuk.