Governing body SANZAAR said Tuesday that 20-minute red cards will be among the rules changes for the 2024 Rugby Championship, which starts Saturday.
In certain cases under the new rules, players sent off after being shown a red card can be replaced by another player 20 minutes later.
The rationale is that individual players, not the match, are punished for some red card offences, SANZAAR said in a statement.
However, deliberate foul play with a high level of danger will still result in a full red card for the offending player, who can neither return nor be replaced, SANZAAR added.
The tournament kicks off with Australia hosting world champions South Africa in Brisbane on Saturday.
Holders New Zealand face Argentina in Wellington later the same day.
A countdown clock of 60 seconds for kickers to take conversions and penalties is among the other rules changes being introduced this season.
Forward packs will also have 30 seconds to form a scrum or line-out.
The new laws also include extra protection for the scrum-half, who can't be tackled within a metre at the base of a scrum, maul or ruck.
The referee will be allowed to let play continue for a crooked lineout throw under the changes if the defending team does not contest the ball.