Yes, pretty much so, Simply create a MS document with all the functions you want to use. They are are the form:
You can have as many of these as you want in a given document. Save the document and also compile the document. Whenever you want to use those functions, just add an Include("theFileName")
It is important to have both a regular MS document and the compile version saved. Only compiled versions can be included and compiled files cannot be edited, so you'll want the original document to make any modifications you might want to make.
Also, compiled functions can call other compiled functions and you can have as many includes are you want in a given document. So code away!
And just to clarify, you can make simple functions in MS, say:
f(x) = sin(x)
That is not the sort of function I mean. Callable functions in complied scripts use the @form I noted in the above.