So Rick that shoots down swapping lock cylinders and keeping the new dust door. Can a locksmith re-key a cylinder somehow. Sorry if that is a stupid question but no knowledge on the matter. The only other way I can see getting a matched set is buying every lock as a set and that is over $800.00. What a bitch!
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Spending $800 for matching keys is out of the question.
Please tell us why you're changing locks. Was the original damaged, stolen or what. Knowing why the knowledge is being sought will help us all better understand your dilemma.
It's been a long time, but I think I once took a lock to a locksmith and had him change the lock to fit a specific key. I assume that one of the bags needs the lock changed (for a reason to be supplied by you) and that the other bag is ok. Take the good bag, its key and the new lock (if you have indeed purchased it, this is why we need particulars) to a competent locksmith and ask him or her what the possibilities are. I did state competent locksmith so if the first one tells you it can't be done, consult others. There are competent and incompetent people working in all professions.
Rick's reply included the proper name for the dust door. Is this the part that is damaged? If it is and you just want to replace it to be able to use the same key in all locks, then take the damaged lock and the new lock with the good dust door but the wrong key, to the locksmith and I'll bet he can readily solve your problem.
These answers are all based on assumptions because your questions did not supply enough information for us (me, for certain) to accurately diagnose the problem and offer suggestions. Please keep us current as we sincerely want to assist one another. Also, please post the exact nature of the problem so none of us are left in the dark.