As to the eruv: my husband’s family doesn’t hold that the eruv is treif, but they don’t use it. I’m not the only person I know to get this psak.
But here is another (less objectionable LOL) example.
Growing up my school and shul davened nusach ashkenaz. My father’s family davened nusach sephard. I never felt quite comfortable because everyone I was davening (school and shul) was ashkenaz. I spoke with my Rabbi who told me I was allowed to daven in Ashkenaz.
Fast forward: I got engaged to a guy who davens sephard. I never felt comfortable davening sephard. So I asked the Rabbi and was told I could continue davening ashkenaz.