@Popa: “Who says you have a right to be frum on yenem’s cheshbon? Suppose you don’t have tefillin and only your neighbor’s wife is home? You have to knock on the door, ask for the tefillin, and put them on. And deal with your nisyonos. You can’t not do mitzvos because you have nisyonos.”
Without careful application of the עשה דוחה לא תעשה dictum, you are not allowed to be oiver issurim in order to be mekayem mitzvos. (Regardless of חלל שבת אחת כדי שיקיים שבתות הרבה.) The ends certainly do not justify the means. In your specific case – putting yourself in a situation of nisayon – the Gemara (BB 57b) classifies אי דאיכא דרכא אחרינא רשע הוא, אי דליכא דרכא אחרינא אנוס הוא. This would (probably) be ליכא דרכא אחרינא. (I don’t understand that Gemara at all, so I’m not sure I can apply it to cases other than the Issur Histaklus. I have not seen the Gemara bought down anywhere in Shu”a or Ramba”m. I would appreciate it if somebody could point to a source which brings down a halachic distinction of Leka Darka Achrina)
But in any other case, to be oiver an issur is absolutely NOT permitted in order to be mekayem a mitzvah. And if you are aware that it isn’t a nissayon but is an issur, then you would not be permitted to do the mitzvah.