you can definitely apply ex-novo for BCG – they may still have your previous application registered but they will not consider it as a direct reference, given the time difference.
As for the application, I would try to focus in particular on two things:
- Show a strong fit with the niche practice you mentioned, to emphasize the value you could give compared to other candidates.
- Find a referral to strengthen the application. There are far less slots available for experienced hires compared to MBA graduates, thus, unless you have a strong introduction, it could be even more challenging to be considered for an interview now then before.
Once received an invitation, you may also want to have a clear explanation of your progress since the last application, as a backup in case they ask about that.
Hope this helps,