Welcome to TheSwamp!
Not sure what version(s) you're now using, but is there any chance of moving to Annotative Scales instead?
I ask, as changing a drawing's Model, or PViewport annotation scale automagically modifies linetype and dim-scales for you... To test for yourself, use LTSCALE == 1, MSLTSCALE == 1, and PSLTSCALE == 1 (and some pre-defined annotation scales, of course).
[Edit] - This would also allow you to use the in-built UI, precluding the need for a custom dialog.
Example:
Command: SYSVARWATCH
SYSVARWATCH = ON
Command:
Command: _CANNOSCALE
Enter new value for CANNOSCALE <"1" = 20'">: 1" = 30'
[SysVarWatch] : System Var Changed : DIMSCALE = 30.0
[SysVarWatch] : System Var Changed : CANNOSCALE = 1" = 30'
Command: SYSVARWATCH
SYSVARWATCH = OFF
Command:
Cheers