mitch: doesnt nuclear decay refers to the nucleus specifically?
"Electron capture is a type of beta decay in which the atomic number is decreased by one unit, as in positron emission, but in this case by spontaneous incorporation into the nucleus of one of the atomic electrons (most often one from the K-shell of the atom)" (Friedlander - Nuclear and Radiochemistry).
The probability for this type of decay depends partially on the electron density around the nucleus, so theoretically one should be able to influence the life time by changing the electron density. There have been a few experiments in the past, but the effect is very, very small. It is still not completely clear whether the measurements were accurate enough to see a change in decay rate.
There have also been attempts to change the life time of gamma decays using lasers to stabilize or destabilize energy levels. But these experiments have been inconclusive as well.