I'm applying to transfer, and am filling out the Common App. Should I put Yes to disciplinary action?
This is likely to be closed, as we do not discuss undergraduate admissions here. Still, I'll take a stab at it. 

My understanding is that the whole point of "expungement" is to allow you to answer no to questions like this (unless the question specifically says to include expunged matters, as is sometimes the case, e.g., with law students). That's certainly the case when  legal matters are expunged; I assume it is the same for in-house educational matters. 

Still, I would recommend doing two things:


Don't just "assume it was removed from my record" -- verify. Ask specifically whether other colleges who request your records will learn about this. Note, this is the kind of thing where it's easy for someone incompetent to just say "nope, it won't show up" to get you off the phone -- so keep asking questions until you're really satisfied. Getting an in-person meeting with a career employee (not a student worker) or the associate dean might be better than just calling on the phone and asking the receptionist. 
Contact the college you want to transfer to (anonymously, if you like) and ask whether they require you to disclose expunged matters on the common application. 


If you can get it in writing that you don't have to (and save this
reply in permanent storage), that should be sufficient to protect you
if you are accused of anything later. 
If you discuss this over the
phone and are told not to report it, but can't get it in writing,
send admissions an e-mail, in which you say "This is just to confirm
what I discussed on the phone with Name at 8:00 AM on 12/1. As we
discussed, expunged disciplinary matters need not be reported on the
common application for transfer students. Please let me know if this
is incorrect." Then retain this e-mail and their reply, if they send one. 



As to the second part of your question, yes, if reported this could certainly adversely affect your changes of admission (and improperly concealing it could lead to your degree being revoked).