Hmmmm, thats tricky.
Basically, ALL of the implants are re-programmable in one form or another…
Are you referring to the UID / NUID ( Basically the ID number ) or user memory?
The Low Frequency implants using a T5577 Chip can have their ID changed and their mode ( HID, Indala, EM … )
Something like this would be what you would need / want
xEM
Next Implant
FlexEM
…
In High Frequency, the M1 chip is referred to as a Magic Chip. it is older HF tech, and it can have its ID changed, these m1 chips also have 1kB memory
something like these
xM1
FlexM1
…
If you are referring to being able to write data to one, pretty much any HF implant will do this as NDEF data and you can write to them with a NFC capable phone.
It would be easier for us to recommend something to you if we knew exactly what you wanted to use it for/on.
Knowing nothing else, and if you just wanted to get stuck in, it would depend on your budget, but personally, I would suggest at a minimum
A Next Implant
then if you wanted to combine shipping grab an
xM1
With these 2 implants and 3 chips, you have MOST situations covered.
Both are the small “easy” to install glass implants.
Then if your budget allows, A good addition to your shopping list, is a Proxmark3
NOW, you would be set up to read / write, interrogate, change ID’s and Emulation modes…
Anything after this would likely be case-specific…
That should be enough to get you started on your journey.
If you need more info, just sing out…
You also have the answer for the person who asks you “What do you want for Christmas?”