Yes and no.
There is a fixed and sometimes rather low limit for the length of the resulting (evaluated) menu command - it is 256 characters (longer evaluations will display Diesel error "$(++)". So if you use plain AutoCAD command sequences (no Diesel), you can type only 256 characters in your menu macros.
But there is no such limit for the length of string that a Diesel-enhanced menu macro (CUI file item) can contain - we have successfully tested Diesel macros over 3.000 characters long.
The 256-character limit applies only to the evaluated string (if you use Diesel). An example:
- The menu macro $M=$(getvar,USERI1) is itself 19 characters long but evaluates e.g. to "0" (1 character)
- The menu macro ID;\ is 4 characters long and evaluates also to 4 characters (nothing to evaluate - no Diesel)
(Testing performed on AutoCAD LT 2008 in Windows Vista.)