The pair will now remain with the club for the maximum 93-day period permitted under short-term loan regulations — taking them to Boxing Day when the Pilgrims entertain Lowestoft Town at The Jakemans Stadium.
Tempest (20) made four appearances during his first month with United, while Dixon (19) made six outings to add to the five appearances of his first loan spell with the Pilgrims last season.
Both players have been granted permission to play for United in the FA Trophy.
Elsewhere, the Pilgrims have signed former Rotherham United striker Zeph Thomas.
Thomas (24) is a St Kitts and Nevis international and recently scored twice (against Dominica and Guyana) in three appearances for his country.
He netted a hat-trick for the Pilgrims’ under-21s on Tuesday evening and is eligible to face AFC Fylde on Saturday.