[openbox] Can I dynamically change a client window's role?

[Parke]

I would like to dynamically change the actions a window performs in
response to certain keypress and mouse events.

Specifically: I want to make certain windows ignore mouse drag events
(but only some of the time).

I believe I would be able to implement this result if I were able to
dynamically change the client's "role" (_OB_APP_ROLE).

So, my question is:  Is it possible to dynamically change the
_OB_APP_ROLE property for a pre-existing client window?

Thank you.