You can modify the Salesperson Code and the Contact No. of an opportunity together with the Salesperson Code and the Contact No. of to-dos related to this opportunity.
Open the 
Salesperson/Purchaser
Card window.
Find the salesperson assigned to this opportunity and click Salesperson/Purchaser, Opportunities.
On the Opportunity List
window, click Opportunity,
Card.
On the Opportunity Card
window, change the value in the Salesperson Code field. If there is one or
more to-dos which contain the value you are going to change,
confirm the subsequent message: “Do you want to change Salesperson
Code on the related open To-dos with the same Salesperson
Code?”
For to-dos of type Meeting, the Meeting Organizer will not be changed if the Salesperson Code being changed is the code of the Meeting Organizer.
For to-dos of type Meeting, where the old Salesperson Code is an attendee: this Attendee will not be updated with the new Salesperson Code if there is an Attendee with this new Salesperson Code already participating in the meeting.
Open the Salesperson/Purchaser
Card window.
Find the salesperson assigned to the opportunity and click Salesperson/Purchaser, Opportunities.
On the Opportunity List
window, click Opportunity,
Card.
On the Opportunity Card
window, change the value in the Contact No. field. If there is one or more
to-dos containing the value you are going to change, confirm the
subsequent message: “Do you want to change Contact No. on the
related open To-dos with the same Contact No.?”
For to-dos of type Meeting, where a contact whose Contact No. is being changed is an attendee: the attendee will not be updated with the new Contact No. if there is an attendee with this new Contact No. already participating in the meeting.
Creating Quotes for Opportunities