Hi Phil,
Where is the variable declared? Is it declared on htm page? If yes then there is no way that the value of this local variable can be changed anywhere other than this page itself.
If you are trying to figure out why some field is editable/ non editable based on this field then you are probably going in wrong direction. This variable would probably not responsible for setting 'read only' property.
I would be able to comment more if you can share the htm page code.