CAD tip # 4241:

With SysVarLock you can force users to keep certain AutoCAD settings enabled or disabled or limit values of certain variables.

So you can e.g. deny changes of the PICKADD variable, enforce using the 'internal' MText editor, not allow tracing, not allow switching off the Int osnap, etc.

The SysVarLock application can be downloaded on Download, see description and examples in the accompanying documentation (definition table, the SysVarLock command).

The definition table SysVarLock.tab defines the protection of given variables. See samples:

;format:
; "name-of-variable" test-expression
;
; parameters:
; - name of the variable to lock/keep
; - optional test expression: 'keep these values, disallow others' (expression in LISP syntax)
;
; variable is not changed when test-expresion evaluates to FALSE/nil
; the '?' character is a placeholder for the current value of the variable
; make sure you use the same data-type as the watched variable in your expressions (string, number)
;
; examples:
;  "MIRRTEXT" nil                                  --- never change MIRRTEXT (simple format)
;  "PICKADD"                                       --- never change PICKADD (even simpler format)
;  "UCSFOLLOW" (= ? 0)                             --- never set UCSFOLLOW to 1
;  "AUTOSNAP" (< ? 8)                              --- Autosnap must be always <8 (no polar tracking)
;  "MTEXTED"  (or (= ? "Vnitøní")(= ? "Internal")) --- allow only internal MTeditor
;  "CECOLOR"  (< ? 10)                             --- don't use subtle color hues (only the basic colors)
;  "FONTALT"  (>= (strlen ?) 5)                    --- alt.font filename must be at least 5 chars long
;  "DONUTOD"  (> (+ (getvar"DONUTID") 1) ?)        --- donuts must have outer diameter at...
;  "DONUTID"  (< (+ (getvar"DONUTOD") 1) ?)        --- ...least 1 unit larger than inner dia
;  "OSMODE" (zerop (logand ? 8))                   --- don't allow to set the NODe osnap
;  "OSMODE" (zerop (logand ? 128))                 --- don't allow setting the PER osnap
;  "OSMODE" (/= (logand ? 33) 0)                   --- don't allow to switch off both the INT and END osnaps
;  "LUNITS" (= ? 2)                                --- don't allow to switch to other units than Decimal
;  "BLOCKEDITORLOCK" (= ? 1)                       --- keep Dynamic Block Editor locked (dblclick=refedit)