Is it acceptable to swap out stories from the current sprint to the backlog and replace them with stories of the same estimate size from the backlog, because of changing priorities in the business?
My opinion/experience tells me that this is an absolute no-no and that if the business needs to change, let's say, 70% of the work in the current sprint then we should abort the sprint early and start a new one - with a new commitment.
For the official answer, I'd take a read in the Scrum Guide under The Sprint, including Cancelling the Sprint. (https://www.scrumguides.org/scrum-guide.html#events-sprint)
Scrum does allow for clarifying or renegotiating the Scope of the Sprint, as long as it doesn't put the Sprint Goal at risk. That said, I can't imagine that you can switch 70% of the sprint backlog without putting it at risk. I would expect that this indicates a change of direction, which is precisely what the Scrum Guide lists as the reason to cancel a Sprint.
