We've talked about exactly this internally (it looks like the bug filed on it is from 2 years ago already ), and I still think it's a good idea! Just a matter of finding the time to get it implemented.
Maybe the custom card and icon could each be an (optionally) transparent image, overlaid on the existing frames.
(Though custom animation would be neat too if you could write multiple images. Or: specify CERTAIN numbered frames to put your overlay on, rather than on all of them.)