Keeping the value of a signature after running a predicate/ function?

Question

I have been working on a project using Alloy, I have created a simple add function and what I don't know is how to make sure that the signature keeps it's value after the run:

example:

one sig c1,c2 extends Customer{}

run{
c1 = Create_customer[]
c2 = add_node[c1,node]
}

if you know more about this or have any related documentation or examples, I would be grateful.