There's no law against wanting
to correct your error.
Interestingly enough, the laws don't seem to directly address a POOT by the declaring side. However, Law 45C2 says "Declarer must play a card from his hand held face up, touching or nearly touching the table, or maintained in such a position as to indicate that it has been played." So Declarer's Jack is certainly a played card. Can he change it? I don't think so. 47B speaks of changing an illegal play, but the play of the SJ is a legal play, albeit out of turn. I can't see anything else that would allow a change.