Split stays I've done in the past had the option to decline on both orders. For our split stay coming up in a few weeks I had the option to decline either set before each stay's 31 day mark. If you didn't have the option to decline either set of bands, and you're more than 31 days to check in on the stay/order you're looking at, then its probably just a system glitch.
ANY Magicband linked to your account can be used for any stay, even if you have old ones. So even if you are forced to order two sets of bands, no worries, just use whichever color you like better
It will work for both parts of your stay. I'm collecting colors so I don't decline the free bands
I have many special edition bands purchased over the years that I use for on-site stays, rather than the solid color bands.
Does anyone buy themselves a magic band once at Disney and then connect it to your account and use it? If so, how successful are you? How long will that magic band last for?
Yes, I've purchased many of the special or graphical bands at the parks. I have over 25 linked to me in my My Disney Experience Account, and I can use any one I want, whenever I want.
As for how long they last... Keep in mind that Magicbands have two RFID transmitters inside the "ICON" (some call it a puck, but its the part with the Mickey Head on it).
One is for short range, like where you tap the band, think park entry, fastpass queue entry, photopass, if staying on property it includes unlocking your room's door, pool entry, purchases, etc... The short range doesn't rely on battery and will continue to work as long as Disney uses this technology. So I could use my first bands from 2014 to tap if I wanted to.
The other is for long range, like auto-linking some ride photos and videos (Pirates, Seven Dwarfs Mine Train, etc), finding you with your food for Be Our Guest breakfast/lunch, putting your name on the sign near the end of Its a Small World, etc. This long range RFID relies on a battery inside the band that can not be changed. The battery is said to last about 2 years, but no one has been able to tell me how to test it.
With MagicBand 2.0, you can also swap the ICON from one strap to another. So you could take a new icon from a solid band and put it in the older graphical strip if you wanted to.
Since some of my special bands have special lights/colors/sounds at the tapstyles which are tied to the RFID in the icon, so I don't swap them out. Instead, if I'm using an older band and I'm worried about the long range features still functioning, I just take a newer band(which has a good battery) in my pocket or bag, it does the long range stuff. The one on my wrist still does the tapping.
And remember, once a band is assigned to someone, it can't be re-assigned to someone else. So like I purchased a May the 4th band and assigned it to me, I can't now give it to my son to use.