Brit here; I voted “Nope, couldn’t pull if off if I tried” (oo-er missus!).
There’s something about an American accent that’s somehow qualitatively different from a Commonwealth accent. When I was on holiday for a few weeks in New Zealand, I started to unconsciously develop a Kiwi twang, much to my embarrassment when I realised. And when I lived in Oz, I developed an Aussie accent sufficiently well for me to constantly be mistaken for a fellow-countryman by ex-pats when I moved back to the UK. But having accumulated about six months’ time in the US over the years, I’ve never been able to develop any sort of American accent.
I think the real problem is the vowel sounds, I suppose because Aussie/Kiwi vowel sounds are relatively recent spin-offs from my own accent(s), whereas American vowel sounds have had much longer to develop from a more different set of English accents.
Another problem, not directly related to the actual sounds themselves, is the different cultural environment. Aussies/Kiwis and Brits have a surprising amount of cultural baggage in common. Americans vs. the Commonwealth is a much bigger difference. Anyone thinking they know or understand American culture (or rather: cultures) from nothing more than the big or small screens is fooling themselves.
I suspect that I might eventually be able to acquire a decent American accent, though, if I could figure out just how to do it! I certainly have found myself speaking differently when in the US so perhaps the process has gotten (!) underway; just far more slowly than it did for when I was Down Under.