This really isn't a good idea. "Too many vertices in a line" errors ahoy!
Besides, while square-block maps are occasionally nice for nostalgia and as a stylistic change, there isn't call for enough of them to warrant a template.
The line tool is just as easy to use as the fill tool. This template does not make life easier for novices at all.
[12/23/21 update: One new template added that is triangle-based, specifically by taking all the 1-world-unit squares from the unfilled grid template and dividing them into four triangles.] I use pre-prepared templates to make a lot of NEFX maps and I felt it was time to pass them along for anyone else's use.
One of these is used to create many NEFX netmaps, and is a room of 700 1-WU square polygons with pre-textured walls, ceilings, and floors, differential shading, item spawns, and sounds.
Another one is similar but spanning the entire possible map, and may be used for solo maps. Of course, you may want to delete some of the squares.
The oldest one is the same as the second one except unfilled and not configured.