I am not writing with any authority here, just thinking it through… It seems to me that a suppression is a form of prohibition.
If a practice or belief is prohibited, then I would imagine continuing would be a sin. When variant liturgical rites were suppressed at Trent they were forbidden, the priests and communities who used them were not given any other options.
The best way to tell would be to read the exact wording of the declaration, it should give instructions. Do you know where the exact wording can be found? Wiki (not necessarily reliable) states:
In 1965, in the wake of the Second Vatican Council, the Catholic Church began to reinvestigate the story of ‘little Simon’ and opened the trial records anew. Finally declaring the episode a fraud,citation needed] the cult of Simon was suppressed by Pope Paul VIcitation needed] and the shrine erected to him was dismantled.citation needed] He was removed from the calendar, and his future veneration was forbidden,citation needed] but some traditionalist Catholics ignored this suppression and continue to venerate him.
