You might earn more or less miles as you noted. Bag policies are very much aligned between UA and LH, but yes, if you have a UA-coded LH-op flight then UA rules will be on the ticket. UA will have the more generous change policies relative to LH; UA will also be easier to work with in case of schedule changes. LH flights you might be able to get at a discount through consolidators or Amex IAP, that is not the case for UA, but UA you might be able to use 'break from business' (if eligible).