European Competition Player Registration.

Has anyone attempted to register a player for the Champions League for the Knockout Rounds, who has earlier played in the Europa League? or vice versa?

It should be possible under UEFA regulations; you are allowed 3 replacement players, 1 of whom is a 'exceptional' replacement and is allowed to have played in a different European Competition than your own club.

FM09 and previous editions put a blanket ban on anyone who has played for another club in Europe and didn't include this rule, despite it being part of UEFAs regulations for a few years prior to FM09.

As an example: John Heitinga is currently ineligible to play in Europe for Everton, but for the Knockout Rounds he may be registered as the exceptional player, providing Atletico don't drop into the Europa League.