Modifying iCall from TMSH

Hi,
I've created an iCall script from TMSH, but now I have to modify it. Creating a script from TMSH is fine, no problem, but modifying is a bit more troublesome.

(tmos)# modify /sys icall script myscript
Syntax Error: one or more properties must be specified

(tmos)# modify /sys icall script myscript definition
Syntax Error: the script "definition" must be enclosed in { }

I was hoping that the script would open in an editor like it does when you run "create /sys icall script".

Which method is the best way to create and modify scripts?

/eljay