I don't clearly understand what you are asking however I will try to help. You can change a textfield value using scripts such as posted below. Can you post your form on workspaces for us to look at and understand the exact question? Hope this helps or gets you pointed in the right direction.
Here are some ideas. Choose an event based on when you would like this script to fire. To open the script editor press: CTRL +SHIFT + F5
this.rawValue = form1.subformname.table1.textfield1.rawValue;
or
this.rawValue = form1.subformname.table1.textfield1.rawValue + "Detriot Motors";
or
if (this.rawValue == null)
{
this.rawValue = Miami Motor Company;
}