You raise a couple of issues we'll attempt to address below.
You mention a problem that your print job won't "print" when you use Font
Substitution. During our experimentation, we encountered an intermittent
bug with MacWrite. Text imported to it via the Clipboard (copy and paste)
didn't always print, regardless of whether font substitution is on or off.
The print job would appear to download to the printer OK, but the job would
flush without printing (blank paper comes out of the printer). This is a
problem Claris is aware of, and they recommend saving the document to a
text format from whatever application you are using, then opening the file
from within MacWrite.
You state that when Fractional Widths is enabled, font substitution will
not occur. This is a correct response. Font substitution is disabled in
all cases where fractional pixel widths are enabled. The default for
Fractional Widths is disabled. It is the domain of the application to
enable it if desired.
We don't recall ever seeing a utility that will toggle SetFractEnable on
and off, but such a program doesn't make a lot of sense to us, as each
program needs to call SetFractEnable in the Macintosh ROM. One
application's setting will have no effect on another program's setting.
We don't think substituting a bitmapped LaserWriter font will help here.
Aside from the printing problem you report, one possible workaround is to
select Helvetica as a screen font, so no font substitution will be required
at all when printing. To this end, Claris made Helvetica the default font
in MacWrite II. MacWrite has no provision for turning off fractional
widths. However, MacWrite II does have this ability. Upgrading to
MacWrite II may be another option.
Another alternative is to change the document's font to Helvetica prior to
printing, perhaps using a program like QuicKeys to streamline the operation
if desired.