RE: modified field value with 2 different tables field method

If you want to display the name of the selected vendor, do the following:

We assume that your table name is MyTable, and you store vendor account in AccountNum field.

1) Create a display method in your table:

public display dsplVendName()
{
    return VendTable::find(this.AccountNum).name();
}

2) Drag extended data type "Name" in your form

3) Set following properties for this field: Data source: myTable (the name of your data source), data method: dsplVendName

Now the field will always show the name of the vendor account that is selected in the AccountNum field.

Does this fulfill your requirement?