Conversation with friends is natural and organic.
Absolutely we can say in the moment "actually don't go there" or a sensitive friend might pick up my body language and not need it saying.
These are some contentious issues affecting people in my life: bereavement, still birth, infertility, infidelity, depression, mania, psychosis, child abuse, drugs, alcohol, cancer, degenerative illness, fraud, unemployment, gay parenting, suicidal ideation, religion, rape, trauma, disability.
Nobody has ever needed to issue a statement prior to meeting up that we may not discuss a certain topic or timeframe.
My children learn to be compassionate to others from experiencing my compassion towards them. I want them to learn to hear "actually don't go there" and learn to detect social cues and body language.
Saying "never speak of anything before gender identity" is purely about control and the dangerous fallacy that not sharing beliefs = hatred. It prevents natural mutual interactions, genuine compassion, reading social cues etc and ultimately will isolate the child in question from genuine friendships. #bekind it ain't.