RFID Toys : A Few Beginner Questions

The issue with an implant being re-writable is that would mean that regular tags would need to be re-writable as well. Some tags are completely re-writable, like Gen2 UHF tags... however these tags are never used for the applications you want an implant for (ID, security, etc.) for obvious reasons. The premise on it's face is flawed because it would mean the ID/security system would not be reliable or secure. That's why you will never see an implant that can be programmed to emulate another systems' tags.

An implant is most useful to a person who can build their own systems. In some cases, an existing access control system you might encounter at work or school could use a tag type that also can be found in a glass capsule configuration that might be implantable - Not all glass tags are implantable. Some use glass that contains lead and other heavy metals. Research should always be done before implanting something in your body... it's your job to research the safety of these objects, no one else's.

As I was saying, the likelihood of encountering these kind of systems is very low. Either the system uses proprietary technology (like HID and Honeywell systems do) and the tag is not available in a glass capsule form factor, the system uses HF 13.56MHz technology which is not as compatible with implantation as LF 125KHz tags are, or the system does use an LF technology that can be found in a safe implantable glass form factor, but you would then need to convince the system operator to add your implant to the system rather than issue you a card... so the likelihood of you being able to use your implant with a work or school access control system pretty much falls to zero.

With all that said, there is one possibility that exists where cloning could work, that that is in the event you get yourself a Philips HITAG 2048 tag and encounter an access control system that uses EM4102 tags. In that case, and that case only, you could program your HITAG to emulate an EM4102 tag, and change that emulated ID on demand... but I don't recommend bothering. Almost no commercial access control systems use EM4102s and to program the HITAG you would need a special reader/writer and software that can be several times more expensive than a simple reader that works with a basic EM4012 implant.

In short, you will not be happy with an implant. You cannot do the things you want to do with it. There are a few posts on this forum from people with the same goal. If you need an extended explanation, search around for those posts.

"Obviously, an RFID implant would alleviate a number of issues when it comes to key fobs and badges." - this is not correct.

"Can you overwrite a previously clone-written implant" - this is not accurate for LF/HF passive tags. tags come with a pre-written ID that CANNOT BE CHANGED. some may also have writable memory blocks in addition to their ID, but that's separate.

"Can you switch RFID signals on the fly with a device of some kind" - no. some tags have memory blocks that can be updated/re-written using a reader/writer device, but you cannot change "signals" (frequency, protocol, air interface, unique ID, etc.)

Sorry for the brevity, but this has been covered a few times and I'm getting lazy :)