pba said it best as usual. Its very common for BT’s to go past what they are ready for. Unfortunately the feeling of “overburdened” that comes from moving too far too fast has caused many a BT to fall back down.
When I spoke to my R”K about taking on a new minhag in my clothing he told me to first discuss it with someone who knows me very well, like a rebbe and figure out why I felt it necessary to make this change. Then after that, to take it on slowly, such as only Shabbos an Y”T etc.
Assuming everything in the your theoretical case was true- especially that his hashkafos are yeshivish to a strong degree in all areas- I would say that its probable that this person would be ready.
But as in any case, the person has to contemplate how he would feel being identified as a “black hatter” and just as importantly in my opinion, how comfortable he feels among other “black hatters”.