Dynamic change user-defined field

Yes. On the project custom field. On the Receipt - user-defined field

protected void EPExpenseClaimDetails_ContractID_FieldUpdated(PXCache cache, PXFieldUpdatedEventArgs e, PXFieldUpdated InvokeBaseHandler)
        {
            if (InvokeBaseHandler != null)
                InvokeBaseHandler(cache, e);
            var row = (EPExpenseClaimDetails)e.Row;

            PM.PMProject project = PXSelect<PM.PMProject, Where<PM.PMProject.contractID, Equal<Required<PM.PMProject.contractID>>>>.Select(Base, row.ContractID);
            if (project == null)
            {
                return;
            }
            var pmExtension = project.GetExtension<CD.PMPECSTFLD.CDPMProjectExt>();
            if (pmExtension == null)
            {
                return;
            }
            cache.SetValueExt(row, "AttributePROJEXEC", pmExtension.UsrCDExecID);
        }

This code works wrong, I think because selectors. I am getting wrong value CDPMProjectExt from project. Or I should understand how find employee with this selector ID. For example I set up employee ID 1, but from the project selector I get value 123
Also, did you create a CacheExtension for the Expense Receipt? - No, I didn’t. Can it help me?

CDPMProjectExt:

namespace CD.PMPECSTFLD
{
    public class CDPMProjectExt : PXCacheExtension<PMProject>
    {
        public CDPMProjectExt();

        [Owner(DisplayName = "Project Executive")]
        [PXDefault(PersistingCheck = PXPersistingCheck.Nothing)]
        public int? UsrCDExecID { get; set; }

        public static bool IsActive();

        public abstract class usrCDExecID : BqlType<IBqlInt, int>.Field<usrCDExecID>
        {
            protected usrCDExecID();
        }
    }
}

‘Project Executive’ attribute configuration

Thanks for the tip, I'll look in that direction.