According to the PMBOK Guide, 7th edition, one of the project management principles is to "engage stakeholders to understand their interests and needs". This means that the project manager should communicate with the stakeholder and clarify the scope, objectives, and expectations of the project. The project manager should also explain the impact of the stakeholder's interruptions and changes on the team's performance and morale, and negotiate a mutually acceptable way to handle the stakeholder's requests. The project manager should also update the stakeholder register and the stakeholder engagement plan to reflect the stakeholder's influence and engagement level, and monitor the stakeholder's satisfaction throughout the project. References: PMBOK Guide, 7th edition, page 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23,
24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48...

In project management, it's crucial to understand the interests and influence of all stakeholders to ensure the project's success. The stakeholder assessment matrix is a tool that helps in identifying and understanding the interest, influence, participation, and expectations of the stakeholders. It's important for the project manager to regularly review and update this matrix as stakeholders' interests and influence can change over the course of the project. By doing so, the project manager can ensure that all stakeholders are properly engaged and their interests are taken into account, which is key to the successful completion of the project.
The Project Management Professional (PMP) Certification from PMI1, PMP Examination Content Outline - June 2019 - Project Management Institute2, Professional in Business Analysis Reference Materials3.

Agile project management welcomes changes in scope, but it also requires a trade-off of other items in the product backlog. The product owner owns the backlog and has to be able to make these decisions regarding trade-offs between stories and features. The project manager should guide the agile team to add the new scope to the product backlog and prioritize it according to the project goals and customer value. The project manager should also conduct regular backlog grooming sessions to assess and update the backlog items. The new scope should not be added to the current sprint, unless it is small enough to be completed by the time the sprint ends and does not affect the sprint goals. Creating a parallel sprint, pausing the sprint, or moderating the expectations for sprint quality are not agile practices and would compromise the project's agility, quality, and delivery. References:
* How Agile Addresses Changing Project Scope
* Agile Twists & Turns: How to Handle Scope Changes
* How to change your project's scope (the right way)
* Agile Scope Management: Refactor Your PMP

When a new deliverable is proposed, the project manager should evaluate its impact on the project's scope, time, cost, and quality. A cost-benefit analysis is a systematic approach to estimate the strengths and weaknesses of alternatives and is used to determine options that provide the best approach to achieve benefits while preserving savings12. It involves comparing the expected costs of project actions to the expected benefits in order to choose the best option3.
References:
Project Management Institute. (2021). A Guide to the Project Management Body of Knowledge (PMBOK Guide) - Sixth Edition.
ProjectManager.com. (2023). Cost-Benefit Analysis: A Quick Guide with Examples and Templates1.
Wrike.com. (2023). Cost-Benefit Analysis in Project Management Explained2.
Project-management.com. (2023). Cost Benefit Analysis - Formula, Example & Definition3.

Schedule reserves are the amount of time allocated for unforeseen risks or delays in a project. They are usually calculated based on the level of uncertainty and complexity of the project. In a hybrid project, where both agile and predictive approaches are used, the project manager should reconsider the necessary schedule reserves based on the progress and performance of each module. By doing so, the project manager can identify the critical path, prioritize the work, and adjust the schedule accordingly. This can help to take the schedule back and accelerate the ROI of the project. References: PMBOK Guide 7th Edition, Chapter
8.3.3.2; Agile Practice Guide, Section 3.2.2.