To answer your question, yes you can!
We were wondering this as well and called Disney to get an answer. If you got the pamphlet or paper in the mail about the Magic Bands then you know it says that you have to have them customized by a certain day in order to have them mailed to your home before the trip. (It doesnt actually tell you that if you're okay with not having your name or a specific color on them, you can pick up generic Magic Bands when you check in and imput your selections and passes into them then).
If you have a will call number or some sort of verication number for the purchase of your tickets (itll just be one number no matter how many tickets youve purchased), you can enter that when customizing your band and itll pull up your tickets and imput them into your Magic Bands before theyre sent out. So everything will be all set already. Tip here, make sure you accurately include the ages on those traveling in your party, so childrens tickets sync with children, and adults with adults.
You can also customize your bands and include everything you need (resort reservations, fastpass, dining, etc) and not include your park tickets until you pick them up and can imput them. It works just fine and the bands are still mailed to you and customized, just add the park ticket once you pick them up (you can go online, use the My Disney Experience app, or have it done at guest relations for you).
We were also told that customization depends solely on your resort reservations, not your tickets. We purchased the Premier Passport which is like an annual pass for every Disney park int he country, but when trying to schedule dinning reservations and fastpass times using the MagicBand system for the day before we checked into our resort and the day after we checked out, it wouldnt let us.
Also if your stay is split between more than one resort, youll get a band for each person for each resort. We're staying 10 days between Saratoga Springs and Animal Kingdom and all the Magic Bands that showed up on my doorstep scared me at first glance!
Hope that helps some.