I just had a BCG Final Round Interview and it was a narrow miss (case studies and personal fit good, communication should have been more professional, apparently). Considering I'm about to complete another degree with a compulsory consulting internship from a top business school, I was told by the BCG Principal giving feedback that I should apply again in 6 months - I guess this means that I could also apply for McK a second time then as well.
I haven't so far applied to Bain just because it is quite a bit smaller in Germany (where I'm keen to be working) with fewer projects to select from, so it's something of a 2nd choice (though at a very high level). I'm going to apply to Bain now anyway, but in case I get an offer, I'm just curious whether and when it would be possible to switch from Bain to BCG / McK later if they continued to appear more attractive and how difficult that would be.