This is the process that I used to make this one and my "Classic" Link
You will need:
1 Amiibo (I used an Animal Crossing one as they are on clearance at Gamestop)
1 NFC Tag coded with whatever Link you want to use (8-bit for Classic Link and Skyward Sword (SPOOFED) for Skyward Sword Link)
1 Medicom Legend of Zelda Figure (The 3 available currently are Classic Link, Toon Link and Skyward Sword Link)
Air Hardening Clay
2 Small Screws
Superglue
Zelda Amiibo Label
Gold Pinstripe
The Process:
Tear apart the Amiibo from the base and remove the Existing NFC Tag
Put air hardening clay in the holes left on the top of the Amiibo base.
Sand the crap out of the top of the base to make smooth
Print out the Zelda Amiibo Label (I printed it on Sticker paper and covered the paper with Clear Shelf Liner), and attach it to the Amiibo Base top
Take the Medicom Link and mark where the holes in his boots are on the base top and drill two holes in the base.
Cut out any plastic on the underside of the base top to make room for the small screws
Attach Link to the base with the screws
Put the new NFC tag in the base
Superglue the top back into the bottom
Add Pinstripe to the base if you want
It is really quite simple, and make for a custom amiibo that fits in with the real ones.