Hi Deana,
Thanks for visiting the Disney Parks Moms Panel with your question. At this time, the only customization that you can do to your MagicBands in advance is to choose the color (grey, blue, green, yellow, red, pink or orange) and the name that is imprinted inside the band.
If you want to decorate your MagicBand, there are accessories available for purchase at the Disney Store and at Walt Disney World merchandise locations. Those include covers and charms. It might have been a MagicBand cover that you saw. I don't recall seeing a Tigger cover in the MagicBand merchandise displays on my last visit, but I'm sure new designs are being released frequently.
For example,
Frozen fans were excited last week when Walt Disney World announced that MagicBands preprinted with images of Anna, Elsa or Olaf are now available at
Wandering Oaken's Trading Post at Hollywood Studios.
Please let us know if we can answer any other questions for you as you make your plans for your Walt Disney World visit. Enjoy!
Wilma