Dear/ Hello [Name], - запятая, не восклицательный знак
I am writing to request additional hours for our current project. Our customer's requirements have recently changed, and we need to allocate more time to ensure that we meet their needs. - тут, конечно, нужно больше деталей. Что изменилось? Почему?
I understand that this request may require adjustments to our current agreement, and I am open to discussing any necessary changes with you. Please let me know if this is possible and what steps we need to take to move forward.
Thank you for your understanding and cooperation. Hope to hear from you soon.
Best regards,
[Your Name]