Actually my request to you was more to do with the Yekkishe minhag. Let’s say a baal tshuva or a ger joins the GGBH or Breuers. From the way you answered I would think you’re saying he would take on the minhag hamokom.
Why would this be different to any other machlokes haposkim?
How do they deal with someone who is not noheg to wear tfilin if he comes in and davens?
I have seen it before in GGBH and I didn’t notice any reaction. There was a reaction, however, when a non-regular who davens in a minyan where they don’t wear tefillin came to GGBH because he was worried about wearing tefillin there, and he didn’t put on a tallis (he wasn’t married). One of the regulars pointed out the irony of coming here to avoid לא תתגודדו and still not wearing a tallis.