Constructive empiricism is the belief that science aims to give theories which are empirically adequate (i.e. agree with observables), and accepting a theory means believing that it is empirically adequate.
Instrumentalism is the belief that the value of scientific theories is measured by the extent to which they help us make empirical predictions.
Is there any difference between the two? They both would reject the idea that science can say anything meaningful about unobservable entities. They also both seem to agree that there is some sort of reality that we have access to with regard to observables, and that science is valuable insofar as it helps us understand these observables. I don't see any difference.