How to reuse code already written ?

I'm wondering how to use what I think is called "code-branching" to use another procedure I've already written so I don't have to keep

pasting the code again into whatever I'm using now for some specific function. So say for example i have:

procedure( changeShapeTometal2()

   selectedSet()~>layerName="M2"

)

and I have attached that to a bindkey which I use once in a while when the need calls for it.  But now I'm working and I find another

thing that I can automate which will speed up my work, I need to do something like this:

procedure( makeShapesStretchToLeftEdge()

   foreach(shape selectedSet()

       shape~>bBox=list(0:yCoord(car(shape~>bBox)) cadr(shape~>bBox) )

  )

so after the spot where I change the bBox to be at X=0 I want to change all those shapes to M2,  I don't want to add the code to change

the layerName because I already have that written some where , it would make sense to me to just add the procedure call and then

return to where I was,  Do I need to do anything to the original procedure which changes the layerName so once that branch is done it

returns to the code where I am stretching to the left Edge?

Thanks.