Is there such a thing as a rabbinic prohibition of “bal yera’eh, bal ye’matzah”, so that a person can transgress however only m’d’rabbanan?
Perhaps somebody who only does bittul and not bedikah and bi’ur, based on Rashi and the Ran (beginning of Pesachim).
According to these opinions, the enactment of bedikah and bi’ur is to avoid transgressing the prohibition of bal yera’eh.
Somebody who does bittul alone does not transgress the prohibition on a Torah level, but he will transgress, so to speak, on a rabbinic level, for the chametz that he does not know about.
According to certain opinions (see Tosfos Pesachim 42a) there is a rabbinic prohibition of bal yera’eh on chametz nuksheh and ta’aroves chametz.