

The saying “you can’t butter a fly” is an idiom expressing that someone or something is too difficult to influence or manipulate. It’s rooted in the idea that butterflies, with their delicate nature, are virtually impossible to convince to do anything against their will, let alone “butter” them in a literal sense.
An intersex person is typically assigned a gender at birth, but so is everyone else. Being intersex just means you aren’t biologically male or female (though I think this might also include people who have sex chromosomes that develop as though they were the other binary sex, but I’m not an expert). Most intersex people don’t typically know they are intersex, and thus they would count as cisgender so long as they identify as the gender they were assigned at birth and transgender if they do not. Thus, if someone had, say XY chromosomes, but was assigned female at birth, they would probably be cis if they identified as female.
However, trans can be a bit of a self-identifying label, and thus someone in that situation might just as well consider themselves trans. There’s a lot of different definitions for trans. Many non-binary people would consider themselves trans since they don’t identify as their assigned gender at birth.
Long story short, gender is complicated. Sex doesn’t change (put a couple asterisks here), but gender is super flexible (also asterisks here.)