"Lock Design" per form
I see this as a right click on form, toggle Lock Design, and the form (just that one) could or could not be edited (GUI elements can not be moved, components can not be added, etc...)
Gad D Lord commented
It think this can be highly valuable for long-running complex projects with lots of UI controls. I have an 9 year active project and and I barely put a new form or control but yet add functionality behind it.