Would you consider them to be invalid in your eyes?

I don’t consider ‘transracial’ to meaningfully be a thing, no.

Would it warrant disrespecting someone upon hearing they were transracial?

I would not regard a white guy at the age of 25 who decided he was black as black in any meaningful sense, nor would I play along with the idea, no. And, in fact, my opinion of them would be considerably lowered by the fact that they’re misusing racial identity as some kind of fashion statement, that they’re damaging the very real struggles of black folk by doing so, and by the fact that the very idea of transraciality shows a severe paucity of understanding of what race is and means in modern society.