The best practice for handling an urgent, high-priority change request in Scrum is to add it to the prioritized backlog for the next sprint. This way, the change request can be reviewed by the product owner and estimated by the development team before being added to a sprint. Adding a change request to an ongoing sprint would disrupt the planned scope and schedule of work.
References:
* https://trailhead.salesforce.com/en/content/learn/modules/salesforce-business-analyst-certification-prep/ma
* https://www.scrum.org/resources/blog/how-handle-change-request-scrum

The first step that the business analyst should take to begin overhauling the Opportunity object is to understand the current business process. This is because understanding the current business process helps to establish a baseline for measuring the current state of performance, identify pain points and opportunities for improvement, and align with the desired business outcomes. The business analyst should use techniques such as interviews, observations, surveys, or process mapping to understand how users currently use Salesforce opportunities and what challenges or gaps they face. References:
https://trailhead.salesforce.com/content/learn/modules/salesforce-business-analyst-certification-prep/business-pro

Working Hours is not a Locale Setting that can be selected when creating a new user. Working Hours are set at the organization level or at the resource level for scheduling purposes. Time Zone, Language, and Locale are Locale Settings that can be selected when creating a new user. References:
https://help.salesforce.com/s/articleView?id=sf.users_add.htm&type=5

Explanation
The business analyst should acknowledge the feedback, create a new user story that includes the field changes, and ask the stakeholder to update the existing test case to show it was successfully tested. This is because changing the label of several fields and adding two new fields are new requirements that were not part of the original user story or test case. Therefore, they should be captured as a new user story with its own acceptance criteria and priority. The existing test case should not be modified to include these changes, but rather updated to reflect that it passed successfully based on the original acceptance criteria. References:
https://trailhead.salesforce.com/content/learn/modules/user-story-creation/user-acceptance-testing