Apparently yes! In LibreOffice:
- Click menu Tools -> Customize... -> Keyboard. A dialog like below will show:
Now, to enable switching to "monospace"/"fixed-width" font, via e.g. Alt-1 shortcut:
In Shortcut keys, scroll down to e.g. Alt-1 (was empty for me) and click it;
In Category, scroll all the way down to Styles, click it to open, then click Character;
In Function, choose Source Text;
Click the Modify button (don't forget to do this!). Your Alt-1 should now show in the Keys area (bottom-right).
To enable easy switching back to "regular" font, repeat above steps, but use e.g. Alt-0 instead of Alt-1, and Function Default Style instead of Source Text.
(Based on a reddit answer to a similar question.)
Hints
And by the way, some related shortcuts available by default, apparently:
Ctrl-1, ..., 5 -- paragraph style: Heading 1, ..., 5
Ctrl-Shift-0 / Ctrl-0 -- paragraph style: Default Style / Text Body
F12 / Shift-F12 -- Numbering on/off / Bullets on/off
Ctrl-Shift-P/B -- character style: suPerscript / suBscript
