>>If the file is also part of the .EXE, it would appear as readonly, too.
>
>I guess you nailed the problem. The form has to be excluded from EXE to be modified using USE command. Also why would you want to open scx file in run-time?

I've done exactly that in applications that allowed "customization" to forms at runtime. The custom elements were stored in a table and applied during the form.Init.