i think whoever changes thier nick could use thier signature to let others know.
for example, their signature would say:
"Tigers_eye, formerly known as Cat's_eye, changed nick on 12/8/**"
if they keep that sig for a month or so, the regulars and the active members would surely know by then about the changes and as with anything else, cope with the minor alteration with quite ease.
Verily, in the remembrance of Allah do hearts find rest [Al-Qur'an,13:28]