setvar

(setvar name value)

Changes a system variable and returns the value. Those of the drawing can be undone; OSMODE, ORTHOMODE and SNAPMODE change the program's object snaps, ortho and snap. An invalid value gives the error AutoCAD variable setting rejected.

(setq old (getvar "OSMODE"))
(setvar "OSMODE" 0)
(setvar "OSMODE" old)