Consent during sex questions: Do you have to ask to change positions? Can a “no” become a “yes”?

"Should you ask for consent every time you change position? What if someone has particular positions that they don’t like or have negative associations with?

How do you navigate people changing their minds during a hookup—specifically, when they first say that they don’t want to have sex, but then later they say that they do want it after all? How much should you check that they genuinely want it, that that wasn’t a hard boundary when they initially set it, and that they’re not feeling pressured?..."