In this case the standard definition is close to the usage among communists:
"the doctrine that ideas are instruments of response and adaptation, and that their truth is to e judged in terms of their effectiveness."
an instrumentalist approach to ideas judges ideas by whether they encourage the kind of thought and action desired among people (not whether they are true, i.e. correspond closely with reality).
the 9 Letters to Our Comrades
" argue that Avakian (chairman of the RCP,USA) both condemns and practices instrumentalism:
"Avakian criticized the method of manipulating people by fudging the truth, but his party is jacking people up using instrumentalist predictions. Seeking (once again) to “keep the advanced elements tense,” the party is insisting (once again) that the world is rushing rapidly toward a very specific, irreversible disaster and that only this Chairman and his supporters can save the day."
His definition is this “By ‘instrumentalism’ here I mean torturing reality in the attempt to make a distorted version of reality an instrument of certain aims.” (Avakian, revcom.us)bringing forward another way