This is one of those features we'd planned to do for ages, and customers kept asking us to make script code reuse easier (if FB3 you can include an external script file, but this is less than ideal). FinalBuilder 4 now allows you to have global VBScript and JScript stored in your project file and the script code is available to all actions in the project.
For example, define some global VBScript (access this dialog from the Project menu):
This dialog supports syntax highlighting, code completion, parameter hints and also will display subs, functions, constants, etc in the right hand side section to make it easy to see an overview of your code at a glance as well as easy navigation within the script (double-click an item and it scrolls the code to the right spot).
And then you can use the script as you would a normal function, sub, etc.
(also of note in the above screen shot is that the Run Status tab has been removed and a new Action Information tab...)