There is a way in Workflow to handle this.

In the Script Editor (you need to be a Project level Admin, and this code would need to be in each project where you wan the behavior).

You will need to add code to 2 ''methods'' in the Workflow:

1) in Common Script / Function ActionCanExecute(ActionName) :

Add this code BEFORE the ''ActionCanExecute = True'' line

'The code below will enable R/W on BG_DEV_COMMENTS (defect comments field)
'only when the ''Add comments'' field has been pressed
'code in Bug_MoveTo was added to make the BG_DEV_COMMENTS field read-only by default
if ActionName = ''FieldComments.AddComment'' then

msgbox ''Enabling Comments''

Bug_Fields(''BG_DEV_COMMENTS'').IsReadOnly = False

end if

2) In the Defects module script / Sub Bug_MoveTo :

Add this code AFTER any layout setting code (layout code sets the field properties)
It would be AFTER the line with ''WizardFieldCust_Details'' if you previously used the script generator wizard for ''Defect Details Field Customization'';

'Make sure comments are read-only
'Code in ActionCanExecute will test to see if Add Comments button
'has been pressed before allowing comments to be added.
Bug_Fields(''BG_DEV_COMMENTS'').IsReadOnly = True