Can an FM translator for a full-service broadcast station displace the FM translator for an LPFM station because the full-service station is primary status?

No.  While the full-service station may be of primary status, their FM translator is still secondary status.  A proposal for an FM Translator must make a showing that the proposal's interfering contour does not overlap the protected service contour of a previously authorized FM translator station, even if that FM translator is rebroadcasting an LPFM station.

Section 5(3) of the Local Community Radio Act of 2010 states, in part, that FM translator stations, FM booster stations, and low-power FM stations remain equal in status and remain secondary to existing and modified full-service FM stations.