Thanks for posting this.  I also encountered this and my client, who has used Link for several year, and I just gave up and came up with work arounds for everything.  

Same situation: client had to change a hacked email account.  I got messages that I had to make changes in Link to agree with the new one in the client info in Lacerte.  I have a second Link account because my firm name changed with my business partner retired.  I had to change it in there as well.  At that point I could re-invite, but the questionnaire and engagement letter didn't attach.  

One of the reasons I don't encourage clients to use Link.