Modify Contents of DW Document

Hey I just want to know if this is possible at this point.

I want a button the user can click and it will do a global find and replace on their current opened DW document.

I try doing this and everytime it tells me I cannot modify the document.

Says I gota put it in a behavior and I looked it up and it seems that it can only modify selections well I don't want too I want to modify the whole document.