Replace B&W Nautilus HTM1 tweeter with HTM3S tweeter?

They are not the same tweeter. Not really sure if it is feasible to swap tweeters. If you do swap tweeters you would want to change both tweeters.

My next question is what broke and can you just repair/replace the broken part?

You should call B&W.

Thank you for the reply. You are right the HTM1 tweeter (ZZ11266) and HTM3S tweeter (ZZ14359) are not inter-changeable. I broke the plastic housing around the cone, and I should just replace that instead of the whole tweeter. Problem is bowerswilkins.encompass.com currently shows 60 days lead time to get the part. Thanks.