What happens to Lutherans who become Catholic? This question is a two-parter, I know that's bad form but I don't want to justify two questions.  

Question 1 - if a Lutheran drifts into Catholic beliefs, like the Immaculate Conception of Mary, the Primacy of Peter and a belief in Salvation through Faith and Good Works are they free to do so?  

Question 2 - if they are received into the Catholic Church at some point in time is there formal process of excommunication from the former Church.  I know that as a Catholic they'd be obligated not to take part in Lutheran services but from the Lutheran perspective what does the convert have to give up and what can he or she take?
Lutherans officially recognize the "Office of the keys"


  What is the Office of the Keys?*
  
  The Office of the Keys is that special authority which Christ has given to His church on earth to forgive the sins of repentant sinners, but to withhold forgiveness from the unrepentant as long as they do not repent.
  
  Where is this written?*
  
  This is what St. John the Evangelist writes in chapter twenty: The Lord Jesus breathed on His disciples and said, “Receive the Holy Spirit. If you forgive anyone his sins, they are forgiven; if you do not forgive them, they are not forgiven.” (John 20:22–23)
  
  What do you believe according to these words?*
  
  I believe that when the called ministers of Christ deal with us by His divine command, in particular when they exclude openly unrepentant sinners from the Christian congregation and absolve those who repent of their sins and want to do better, this is just as valid and certain, even in heaven, as if Christ our dear Lord dealt with us Himself.


as given in Luther's Small Catechism from Luther's te, though he may not have written these questions himself. And while there may be some today, and almost certainly some in the past who might have invoked this in the past with respect to someone who converted to Catholicism, it would not be the default action for most Lutherans today, with respect to someone who might choose to.join the Catholic Church as to Lutherans who come to accept certain hallmarks of Catholic beliefs, there is no particular problem with this, either, and it is probably the rare individual who does not agree with at least a few of them, though there are probably some beliefs that are rarely held by Lutherans.