data block item only allow update but no new insert

need some idea on how to handle this.

I was asked to customized a existed form ( oracle form 6i in EBS 11.5.10.2 ).  Add a field called "Email" in the form.  The only value is YES or NO.   Sort of like setup purpose.

When the form is opened, the Email field is populated the value from a custom table ( TABLE_A.EMAIL_COL ).  The TABLE_A has 1 column called EMAIL_COL

TABLE_A

========

EMAIL_COL ( Column )

---------------                

YES

Here is what I need help.  I want ONLY update and query in the Email field in the form.  Not allow insert or add new row into the TABLE_A through the form.  if user update the Email field in the form, it is required to save it back to this row.  The TABLE_A will always have 1 row.