Column in tabular form non-editable on update but editable on insert?

Question

I've got a tabular form and one of the columns should be editable when one chooses insert new row but once the row is created the column should not be editable.
So I want a textfield when creating a new row and a standard report column for the rows already in the table.
Can this be done?
I really need to keep this simple (developmentwise) so it need to be done within apex's tabular form "wizard"...
Thanks in advance
Andreas

Answer 1

This is an alteranative way to do the same
This code has been tested by me in Apex 4.1.1
Step 1 --> Create a Java Script and add it to the JavaScript --> Function and Global Variable Section
One Can get the name by using Right Clicking on the PK field in Chrome and Selecting Inspect Element
function ro()
    var pk_id = document.getElementsByName("f02");
    for (var i=0;i<pk_id.length;i++)
      if(pk_id[i].value!="")
           pk_id[i].readOnly = "readonly";
Step 2 --> Create a Dynamic Action
Select Advanced
Select the Event --> Framework Events -->After Refresh --> Region --> Select Your Tabular form Region
Condition --> No Condition
True Action --> Execute JavaScript Code
In the Code box type javascript:ro()
The box will only make the Existing Rows RO, When one presses the AddRow as the region is not refreshed the user is able to add new data in the text field.
Works with Delete and Cancel as well.