[Greasemonkey] How to disable evil feature on web page?

[John M. Dlugosz]

If the code like that at <http://www.dynamicdrive.com/dynamicindex9/noright3_dev.htm> is included in the content of a web page, how can GM be used to "fix" it?

I'm guessing that GM runs after the scripts embedded in the page, right?  So can I add a statement to reverse the effect of:
        document.oncontextmenu=new Function("return false")

Would it be correct to delete the property, set it to some known proper value, or what?  I really don't know enough about it.

TIA,
--John