I'm unclear as to have you've listen your staff rates within your Contract Data.
If you've listed your staff rates as say, John Smith - Engineer, then you could only apply that rate to John Smith's time within the quotation.
If you had listed the staff rates as just the job title, i.e. Engineer, then any engineer working on the project, that rate would be used.
To borrow a point from Andrew-W-I; the definition of 'Time Charge' includes the words ' ... staff time appropriate to that rate .... ', with the Employer having the right to inspect the accounts and records of Time Charges, which you are obliged to facilitate at any time during working hours.
Hopefully the above answers your question
A similar question regarding rates within the Contract Data was asked here, which may help with your question.