Will it 'make' this person understand? I see now that it's a scare tactic, isn't it? Punishing/penalising. It's like I give them an ultimatum "Don't mention this/try to stop me from doing this..OTHERWISE YOU KNOW WHAT HAPPENS!!" I don't see it as necessary. And there's certainly no guarantee that it'll work and the person won't ever bring said subject up again and/or try to change me.
So I see it as best to just let it go. I must be stable and politely say for instance that I am not interested in whatever it is/I don't see it as necessary for myself personally. I see here there is certainly an aspect of the other in "Well I've been on this planet longer/I am older and more wise/I've been there and done that/I know what is best." I see that in others who have this behaviour. Am I reacting to to this behaviour? No. I just see it as false, because it is lol.
Recently I realised that another phrase I say because I do not agree with another/don't see what they say as necessary - "I don't care." - Lol this phrase isn't a great one. I see that it implies that I have not/will not even consider what the other person is saying. Although personally, that wasn't the case when I said it, at least not lately. Mine was more like "I've heard this before, I don't want to hear it." So I see "I am not interested/I don't see this as necessary/beneficial for me." As the best things to say. Or one or the other etc.
I may have to repeat it a few times, but you know, it'll work eventually, I know it.