Well thanks Carl. I can tell you know what you are talking about and I appreciate advice from someone that knows something.
I intend to use DAP 33 as I have heard that it is the standard for applications of this kind. (I assume newer materials require specialized knowledge and skills; resources I do not have at this time.)
I think DAP 33 is water-soluble, if not I'll use mineral spirits, unless Linseed oil is preferable.
I don't understand the intent of your modification to the 1" Putty Knife. I had intended to "trowel" the glaze into the window by dragging the putty knife "against" the angle of the window frame, and then drag the specially-modified "angling" tool along the run of the window frame, using the plane of the glass to establish a reference for the tool, and then using the angle of the tool to cut through the glaze.
What I see from your text-description is a "scallop" in the center of the Putty Knife, and I don't understand how this shape will help me to get the proper angle for the glaze.
This is very difficult, trying to describe the situation with these windows. I think maybe I haven't explained what I am trying to do adequately.