Automatically update custom fields

in timesheet I added some custom fields to add the project to which the timesheet refers (which is shown with the naming series). then I added another field to show the project name as well. I made a script using add_fetch.
now when I open a timesheet already present I have to re-enter the project to make sure that it also reloads the head of the project name.
is there a way to make the field load when opened, or even better to load all fields of all timesheets once and for all?