A reversal may result from a memory or copying mistake. It may also be introduced temporarily as a test of a scholar's memory. The mere fact that a change was deliberate does not give all such acts the same status.
In a controlled examination, altered chains or texts may be posed as a challenge. If the scholar corrects them, and the testing variants are then restored rather than circulated as hadith, this differs from deliberately corrupting the established transmission.
Essential safeguard: The authentic form must be restored immediately after the test; the altered wording must not spread as authoritative religious speech. A story about testing a scholar does not authorize careless public circulation of false hadith texts.