Structure-changing rule

Definition
Structure-changing rule is a rule which changes already specified information, and renders the output form distinct from the input.

Example
The feature [voice] is distinctive within the class of obstruents, but non-distinctive in the class of sonorants. If there is a rule which devoices obstruents in a particular environment, say word final, this rule will be structure-changing if it changes [-son, +voice] into [-son, -voice].

Links

 * Utrecht Lexicon of Linguistics