Editable Property of a Field

Hello. I've been working in NAV 2013 R2. I created a boolean variable and assigned it in the Editable property of a field in Vendor Ledger Entries page. In the OnOpenPage trigger, I assigned false in the boolean variable. I also created a button assigning true to the variable. But if I clicked the button, the field still is not editable unless I click the Edit List button. I also tried the IncludeinDataset property but still didn't work. I'm guessing this is because of the version because I already did the same thing using higher versions and it worked. Is there any way to make the field editable when I clicked the button even not clicking the Edit List button. Thank you.