The other day I was practising through my Aussie rock setlist, keeping them fresh, and when the sax solo came up in INXS "Never Tear Us Apart" I said to my son "Your mum would love it if you could play this on your sax...do you know all these notes?" After a brief check, yes, it is within his capabilities. "It's E, then an Eb, then..." "Dad, can you just give me the score to look at?" I searched the internet and found a copy. It was a different key signature, but it was MuseScore format so a few clicks I transposed it, and did a quick test play though - hang on, that's not what I play...uh oh!
Sure enough, listening to the recording - I've been playing two notes in it wrong all these years! Hate that! So there's a question - shall I relearn those two notes or just accept that I'm not playing it right? Well anyone with a bit of OCD wouldn't be able to let that go, so I began relearning it.
Relearning is the worst! For starters, you once put effort in, and now, you have to apply even more effort to undo the old and put in the new. If it was just a melody it wouldn't seem like a big thing, but when it is bassline, mid fills and melody on top, you are relying on muscle memory quite a lot to keep it together. I found a resolve for the correct notes (required different fingers) and played the two affected bars over and over again. It started going into my brain, but it required immense concentration. I figure the two bars over and over again for a few more sittings a few days apart and I should be right.
Over the years I've changed bits and pieces in songs here and there, so it's not too bad modifying learnt music. In fact I will go so far as to say that forcing yourself to change bits and pieces in your songs is a good thing - it stops your back brain from doing _everything_ and gives your front brain some work. In songs which are second nature to me I will often slip melody notes an eigth of a beat forward, or backward - for starters it mixes up the song so it's not just the same verse, chorus, repeat; but it seems like a good thing to get the whole of your brain busy while playing.
...but not relearning a mistake. Don't do that. Get it right before you commit to putting it into you brain...as a wise lady once told me, "Practise makes Permanent." :-)