Process of radiometric dating
For organic materials, the comparison is between the current ratio of a radioactive isotope to a stable isotope of the same element and the known ratio of the two isotopes in living organisms.
Radiocarbon dating is one such type of radiometric dating.
In fact, it is possible to shut down electron capture completely—simply ionize the substance so that there are no electrons nearby.
There is a fairly well-known example of chemical state affecting electron capture activity.
That is, electrons can move closer to or farther away from the nucleus depending on the chemical bonds.
This affects the coulomb barrier involved in Alpha decay, and therefore changes the height and width of the barrier through which the alpha particle must tunnel.
The reason is that, because the atomic number is only four, the 2s valence electrons are very close to the 1s electrons involved in capture.
That is, the analysis of the isotopic and chemical composition of the sample has far greater uncertainty than any uncertainty in the decay rate itself.
The major reason that decay rates can change is that the electric field, from the atom's electron cloud, can change due to chemical changes.
In some cases radioactive decay itself can be observed and measured in distant galaxies when a supernova explodes and ejects unstable nuclei.
There are a few effects that can alter radioactive half-lives, but they are mostly well understood, and in any case would not materially affect the radiometric dating results.