I think we can put we can generalize the various YEC "explanations" for radiometric dating in the millions of years into several classes from which we can expand on your explanation.
1) Geologist are just making it up.
That would be stupid to think and thus is not very common.
2) Geologists just toss out results which don't imply a young-earth.
That not much better. That would be fraud. And it would be very expensive fraud at that given that the tests are not all that cheap to do.
3) Geologists just assumed no initial daughter when they don't now that.
4) The rock has lost and/or gained atoms related to the dating method and thus screwing up the result.
Both of these can avoided by the various methods use age-diagnostic diagrams. These include the various isochron methods, Ar-Ar dating, and U-Pb concordia-discordia dating. Since most current published research uses these methods, these "explanations" are not very viable. That methods using different radioisotopes tend to agree also makes
this explanation unlikely.
5) The rate of radioactive decay varies.
This is the last possiblity. Just as for the last explanation, the fact that methods agree make it seem unlikely. This is of course is where the heat and radiation come in. There is a bunch of fun things we can look at.
We could look at the rock itself. Given the age implied by the radiometric date one can easily compute just how many atoms must have decayed to get that result. Multiple that by the amount of energy each decay would have released and we know how much energy has been released. Now divide by the number of years the YECs think this decay took and we would have how much energy the rock was generating. If that number is greater than what it takes to melt the rock (or indeed do anything that would be obvious to notice) then the explanation would be ruled out. Or we could look at the Earth. If the entire Earth did not have this increased rate of radioactive decay the radiometric dates would not be consistent. If the entire Earth did see the same large increase in the rate of radioactive decay then we can use the known quantity of parent isotope existing now and easily compute how much must have decayed as before. These calculations have certainly been done and the consequences are rather dire.
I don't recall the bit about applying it to potassium in the body. But it is fairly obvious that that would work. The human body needs x amount of potassium to survive. Given the rate of decay the YECs ask for, one can calculate how much radiation will be given off by that potassium and determine how that would affect a person. And as it is, a banana is VERY detectable by a Geiger Counter. Lets see 4.55 billion years divided by 10 thousand years is a bit under a half million. So I think we can be VERY generous and say that the YECs will have that Geiger Counter detecting a 100 thousand times the radation from that banana.
The YECs might try to avoid these calculations by pulling another trick: they can suggest that not only the rate of decay was different, but that the amount of heat given off per decayed atom was also different. If they do that then we should mention that they often claim that the universe had very exact physical laws and physical constants required for life to exist. These two arguments are in severe contradiction. One can suggest that some form of "life" could exist with different physical laws and or physical constants, but cannot suggest that any particular person could survive with these being different. Indeed changing the nature of physical reality is going to have profound implications all over the place. Think about the Sun which runs by nuclear processes. If change in decay constants changes other constants then the rules of chemistry will change. I suspect I would rather try to keep Noah & Co. alive in the heat and radiation.
And again, such agreement of methods is unlikely with such an "explanation."
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