Maybe the easiest is to add a new button with the title you want.
The first one is "Jscript" as you asked, the second one is just "JS".
opera:/button/Enable%20javascript,,,%22Jscript%22,%22Checkbox%20skin%22%20%7C%20Disable%20javascript,,,,%22Checkbox%20skin.selected%22
opera:/button/Enable%20javascript,,,%22JS22,%22Checkbox%20skin%22%20%7C%20Disable%20javascript,,,,%22Checkbox%20skin.selected%22
(Copy & paste the code in your URL field, then click on the link of the error page to add the button)