Add further elements to a previously created array?

For instance at the moment I need to write a for loop, with an 'if element' (I assume this can be done with maple)

if the elements satisfy it then I want to add the answer into an array X:=[a1,a2,a3.....] without changing or having to rewrite the data already in X.

Is there any way to do this, or would I have to write the array myself and put all of the elements in at one time?