It should work either way. Cadder's example works on my system. In general it affects only the current parent style.
If you have a separate dimasz set for linear dimensions then this technique won't affect the linear dimasz. For that reason, I avoid setting size variables in child dimstyles.
This also should not affect existing dimensions. Entering such statements acts as an override for future dimensions unless you use (command "dim1" "save"...)
Using templates would probably be a better choice than
using lisp upon opening in any case.
Regards,
Doug
WinXP Pro, Acad2004/ADT