Can we change the items selected from product backlog (Sprint Backlog) after Sprint planning ?
I thought the answer is no, but when i do some mock exams, there's a question is about this, it explains that we can't change it during the sprint! Which is the right answer ?
Would changing the selected Product Backlog items have an impact on the team's ability to achieve the Sprint Goal?
In Scrum, the team does not commit to scope. Instead, teams commit to achieving goals. At the Sprint level, the goal that is committed to is the Sprint Goal. As long as the Sprint Goal is not in jeopardy, there's no reason why you couldn't change the items. However, this can slow the team down and it may be worth spending some time in the Sprint Retrospective to understand why it was necessary (or right) to change the Product Backlog Items selected for the Sprint.
The Scrum Guide says: "The Development Team modifies the Sprint Backlog throughout the Sprint, and the Sprint Backlog emerges during the Sprint. This emergence occurs as the Development Team works through the plan and learns more about the work needed to achieve the Sprint Goal."
During the Sprint:
• No changes are made that would endanger the Sprint Goal;
• Quality goals do not decrease; and,
• Scope may be clarified and re-negotiated between the Product Owner and Development Team as more is learned.
I think it clearly answers the question and seems to be quite reasonable, too.
Thanks for your answers, i'll take my initial answer which is Yes.