Disclaimer: Nothing on this site is intended to be used as an actual ruling in real life, but especially here where it could end up as a matter of life or death please do not take this as any sort of ruling.
Without getting into the details of what level violations would be involved in any given case, there is a responsum (Igrot Moshe Y.D. 3:155) from R. Moshe Feinstein that seems to address the underlying issue of doing something forbidden now in order to be able to help in a potential future case of pikuach nefesh. The question he was addressing was whether a kohen could attend medical school if he would have to be exposed to tum'at meit (which is forbidden for a kohen). Someone had apparently advanced the argument that the prohibition of becoming tamei should be overridden by pikuach nefesh, since, as a doctor, the kohen would be saving lives. R. Feinstein responded to this particular argument (he addressed several other points as well) as follows:
אבל מתיר מצד אחר דפקוח נפש וזהו שטות והבל שלא ניתן לבר דעת לומר כלל שאף אם לא היה שום רופא בעולם ליכא חיוב מצד פקוח נפשות ללמוד חכמת הרפואה דהחיוב דפקוח נפש איכא לכל אדם שיציל חברו במה שיכול שאם הוא רופא מחויב להציל חולה מחליו אבל ליכא חיוב שילמוד חכמת הרפואה כדי להציל חולה מחליו וכמו בצדקה שאם יש לו לאדם ממון מחויב ליתן צדקה אבל ליכא חיוב על האדם לעשות מסחרים ולהתעשר כדי ליתן צדקה
But he permits it from a different angle, that it is pikuach nefesh. And this is folly and nonsense that is not appropriate at all for someone with intelligence to say. For even if there was no doctor in the world there would be no obligation, on account of pikuach nefesh, to study medicine. This is because pikuach nefesh [means] that each person has to save his fellow in whatever way he can – if he is a doctor he is obligated to save an ill person from his illness. But there is no obligation to study medicine in order to save an ill person from his illness, just like by tzedakah where if someone has money he is obligated to give tzedakah, but there is no obligation on a person to engage in business [in order] to become wealthy in order to give tzedakah.
If we transfer this reasoning over to the case here, we should say that just like we don't have to study medicine (and therefore are not allowed to if it violates some other prohibition) because someone might later die that we could have saved had we studied medicine, we also don't have to maintain a working defibrillator (and therefore are not allowed to if it violates some other prohibition) because someone might later die that we could have saved had we had one.
