Bayān al-tafsīr clarifies what a prior expression meant. Bayān al-taghyīr concerns qualifications or connected exceptions that can alter the legal effect of the preceding wording. Not every later statement is mere explanation, and explanation must not be automatically treated as abrogation.
For example, specifying an amount left unclear in an obligation can clarify an existing statement. A connected exception attached to a general admission involves a different legal operation. Conflating them can distort questions of admissions, conditional declarations, and exceptions.
Correction: Ask whether the new wording elucidates the earlier meaning or changes the operative scope of a ruling. Then examine any required condition of connection between the statements.