Actually I have seen some button box players - who learned all on their own (by ear?) with no external help - play the instrument 'upside down' - or with the left and right hands playing the other side. Quite good too.

For small Piano Accordions (up to about 40 odd bass - it's a physical thing) - especially if you had previously learned piano (keyboard skills) I found that they were easy enough to play 'upside down' too - you could play a full size that way - but because there are more things to remember their physical locations, all that practice needed is a bit off putting, especially if you want to get above a certain standard. Also if the box has cute things like 'chin masters', they will be out of reach....

The tone is unaffected.