I did it wrong for ten years / I've been doing it wrong for ten years
Are both forms equally likely to be used?
I have a feeling that, "for ten years etc" sort of calls for Present Perfect (or Past Perfect as the case might be).
Is, "I was doing it wrong for ten years" fine also?
Re: I did it wrong for ten years / I've been doing it wrong for ten years
If you have just learned the correct way, then "Oh my goodness! I've been doing it wrong for ten years" (with the present perfect) would be right.
If your revelation about the correct way was in the past, the simple past doesn't sound wrong to me, but the past perfect would be fine as well.