Users who have a stable setup and who only ever need to toggle between
the themes without triggering a full reload, are better off defining
their own command which calls enable-theme instead of load-theme:
(defun my-modus-themes-toggle ()
"Toggle between `modus-operandi' and `modus-vivendi' themes.
This uses `enable-theme' instead of the standard method of
`load-theme'. The technicalities are covered in the Modus themes
manual."
(interactive)
(pcase (modus-themes--current-theme)
('modus-operandi (progn (enable-theme 'modus-vivendi)
(disable-theme 'modus-operandi)))
('modus-vivendi (progn (enable-theme 'modus-operandi)
(disable-theme 'modus-vivendi)))
(_ (error "No Modus theme is loaded; evaluate `modus-themes-load-themes' first"))))
Differences between loading and enabling.
Recall that modus-themes-toggle uses load-theme.