need to make Text area or notes lines enable or disable

Hi All,

I have a requirement of enabling or disabling data in lines of a text area in CRM web ui

Here is the requirement.

Lets say i have a text area and i saved data in first 2 lines for an object.

if i open the object ...text box will have 2 lines.

now i am editing the object and trying to add 2 more lines in the text.

My requirement is

The moment i click on edit button 2 lines which already has data in the text area or notes are should be disabled

and rest of the blank llines should be enabled to add more text.

It means user usould not be able to edit previous data in text area but should be able to add more data in the text area.

Please guide me how we can achieve this or if we have any existing example in any component please let me know.

Thanks

Pravin