Qutoe from Oomis “This thought leads me to believe that if the person would become liable after the conversion, for doing what then would be considered an aveira for him, that the conversion is absolutely valid, EVEN IF HE DOES NOT LIVE IN A FRUM WAY, otherwise, his status would revert to being a Goy, and he would therefore NOT be chayav. Am I making any sense here? And what is the actual determination? Because one could argue that ANY ger tzedek might be oveir on SOME halacha as we all might be nichshal, so would that render him a non-valid convert?”
I know this was a month ago but no one answered it…I believe it has to do with the intent at the time of convertion. If at the time of conversion the ger intended to keep all the mitzvos then he is jewish and any avieros he does are aveiros – of a yid. If however he never intended to keep mitzvos then he has never a yid to begin with and his aveiros are not aveiros.