The use of concussion substitutes in the SPFL will be allowed on a trial basis from 6 March until the end of the season, after a vote by all 42 clubs.
Clubs will be permitted to use a maximum of two such replacements in a match, regardless of the number of substitutions already made.
The rule change follows an announcement in December that system could be trialled until August 2021.
When a concussion sub is used, the other team can make another change too.
The Scottish FA refereeing department has began to brief clubs on the rule change.
"Yesterday's tragic news that Gordon McQueen has been diagnosed with dementia is the latest reminder of why it is vital we do everything we can to protect those playing our game," said SPFL chief executive Neil Doncaster.
McQueen, 68, has been diagnosed with vascular dementia, with his family saying in a statement they wished to raise awareness.
His wife Yvonne, daughters Hayley and Anna, and son Edward, said he "wants footballers of today's generation to know there may be risks with persistent heading of the ball".
McQueen's former Leeds team-mate Jack Charlton died with dementia last year and it was confirmed in recent months that Sir Bobby Charlton has been diagnosed with the disease.
Three more members of England's 1966 World Cup-winning squad have also been found to have dementia.