Full Idea
If a thing is only instrumentally good or bad, then even when its nature remains the same it might have a different instrumental value if the causal laws of the universe, or of other things in the universe, were different.
Clarification
Things are 'instrumentally' good if they serve a good end, rather than being good in themselves
Gist of Idea
An instrumentally good thing might stay the same, but change its value because of circumstances
Source
W. David Ross (The Right and the Good [1930], §IV)
Book Reference
Ross,W.David: 'The Right and the Good' [OUP 1930], p.108
A Reaction
A bad tin-opener might be instrumentally good if it was the only one you owned, so we don't need to change the causal laws of the universe.