Gadolha; I don’t think many litvishe react negatively to a visibly sefardi yid saying shabbat shalom, especially if they have a aefardi or Israeli accent.
I share the consternation that many have with ashkenazi jews using the American sefardi-esque pronunciation that takes the chisronos of both the ashkenaz and sefardi pronunciations, attempting to make Hebrew as easy as possible. Most MO people are ashkenaz and should be differentiating between a hard/soft tav, komatz/pasach, tzeirei/segol and others.
It’s also frustrating to see people sound the same as irreligious jews who went to hebrew after school programs.