Some 'system' variables are saved in the registry, some are saved in the drawing and some are not saved at all.
NAVVCUBEDISPLAY is not only saved in the drawing but it is also viewport specific and can be on or off in different viewports.
an inelegant toggle (can be assigned to a function button):
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(defun c:nvc ()
(runsilent)
(command ".undo" "begin")
(if (> (getvar "navvcubedisplay") 0)
(command "navvcubedisplay" "0" "navbardisplay" "0")
(command "navvcubedisplay" "3" "navbardisplay" "1")
)
(command ".undo" "end")
(unrunsilent)
)
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