Hearts will only be allowed to use three substitutes in league action this season - while teams in every other division of the Scottish league pyramid will be granted five.
Clubs across the Premiership, Championship, Leagues One and Two were asked to vote on the number of changes permitted during a 90-minute domestic game in line with new Fifa rules on substitutions introduced at the back end of last season.
Top flight sides already approved the plan, which came into force at the start of this season.
However, just three of the ten second tier sides backed the proposals in a vote, while it was near unanimously approved in the third and fourth divisions.
Eight Championship sides were required to approve plans for a maximum of five changes for the rule to be introduced.
Almost all of the 20 teams in bottom two tiers signalled their approval of the new rules, however there was not enough support for the rule to be implemented during the end of season promotion/relegation play offs - which remain at the standard three.
The Jambos will be able to use five substitutions in the Betfred and Scottish League Challenge Cups, with an additional sub permitted during extra-time.
A spokesman for the SPFL said: “In line with last season, FIFA has allowed each league to determine its own rules regarding the use of substitutes for Season 2020/21, due to COVID-19.
"As a members’ organisation, it is important that the clubs in each Division decide issues such as this for themselves.”
Hearts start their season with a Betfred Cup ties against Inverness Caledonian Thistle, Cowdenbeath and Raith Rovers, before their league campaign gets underway at home to Dundee.
