I think it would be relatively simple. I would rehydrate the skin where the leg attaches to the feather of the duck. Once it was pliable, I would cut around the leg with a scalpel, then either snip the wire or bone, or both. The replacement feet could be injected and painted prior to reinstallation. I would bend my wire like a pointed fish hook, and shove it in the manikin, where it would stick in the form, and not pull out easily. Then glue the feather back in place. many guys attach their feet after they are injected and mounted. There is a tutorial in the tutorial section on taxidermy.net showing the process.
With the bird being dry, the operation will take some slight improvisation, but the bird will be light enough to be supported by a heavier wire without tucking the wire like you would when the manikin is exposed (during the initial mounting you did on the duck years ago).
By the way, The USFWS has no issues with you replacing your own duck's feet....we won't get into it if it was a customer's bird and all the technical garbage that would go with that operation lol.
Here is a drawing of what I'm referring to by a pointed hook. This is actually what I do when installing a flying duck foot instead of running the wire through the form, and running it back into the form to lock it in. I just take the wire, and bent the wire to a dull point, and make a barbed piece hanging off to slide in, and not pull out.
- wire for duck.png (4.99 KiB) Viewed 1180 times