After the death of a close relative, a person enters the state of aninut, during which he is exempt from a variety of mitzvot. It seems (from the limited write ups which I have read) that this exemption applies to positive mitzvot ("An onen is exempt from positive mitzvot but can't violate any negative mitzvot.")
According to the Rambam's list of mitzvot, honoring parents is a positive mitzvah. Here, see #59 and 62.
Without looking at specific actions/cases, theoretically, is a person exempt from having to honor a parent when he is an onein?