Does anyone know if you can alter the shape of an already made RFID antenna. I’m just not very versed in the actual inductance and why it has to be a certain amount
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Depends on the type of antenna. PCB antenna might be hard 
With my DIY coils I have made recently I bent a circular coil into a sort of bean like shape and it worked well. I do not understand the science enough to explain the limits / effects of it.
Here is the image of the coil, it was a “perfect” circular spiraled coil.
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Yeah, you can mildly bend it and deform it if you want and retain most of the functionality. Just don’t kink a single strand of wire or the whole thing is fucked.
Figure it doesn’t hurt to explain. The coil needs to be at a specific Inductance value in order to resonate at the target frequency. The farther off it is from that Inductance value, the less efficient the power transmission will be because of signal reflections and power loss as heat.
Luckily, the number of turns in a coil has much more of an impact on Inductance than the shape. You should be able to bend and warp the coil and experience only a small drop in field strength.
One thing that will dramatically change is the field shape, which I suspect it’s why you’re interested in this. For RFID cards, bending the coil is going to greatly reduced coupling efficiency from most angles, because flat reader coils couple well with the flat coils in the card. For implants with cylindrical coils, you might be able to bend it to your advantage. It’s going to be kind of unpredictable, though. You’ll have to test.
Note that repeatedly flexing a coil will quickly fatigue the thin wires and they’ll snap. You could also easily break the flimsy solder connections that hold the coil to the PCB.
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