You can change the width/height of a view by editing its LayoutParams. Example:
View stub = findViewById(R.id.viewStub1);
ViewGroup.LayoutParams lp = stub.getLayoutParams();
lp.height = ViewGroup.LayoutParams.WRAP_CONTENT;
stub.setLayoutParams(lp);
The better question is why you want to do this? Maybe there's a better way of achieving your goal.