Courts change the followed interpretation of law all the time without amending the written law.
Often the written law only gets amended when the difference between the definition on paper and the definition in common practice can no longer be bent any further, after decades of plain conflict in language.
They should not do that either. That’s an usurpation of the legislature’s powers and an affront to democracy.
However I am not sure how that would even work, given the law is in language and language must be interpreted to elucidate meaning from it in the first place. Even if you fixed the first interpretation as sacrosanct, you would then have to interpret that interpretation each time.