I do use .NET, and I do get to read start-end parameters to get length and do things with that info. What I'm interested is that I would like to be able to insert LISP into field, with the ObjectID that I've obtained earlier (from .NET). That way, whatever I put in field during running of my .NET program, would be able to execute and update field on updatefield command. That way, there would be no problem if a user gets DWG, and starts to move objects. Like I said, there is a powerfull %<\AcExpr part in field (I suggest everyone to test that out, it's really cool), and also, there is a LISP.variable part. I was hoping that there is a slight possibility that a lisp (star-end param) could somehow be also included.
I'm just almost sure that this is not possible, but I'm still hoping if someone will tell me otherwise.
(note: for those suggesting using .Length in field - I know, it is a simple solution, but working only for a few curve types)