The Premier League has said it hopes to start permanent concussion substitution trials from January.
The new rule means permanent substitutions can be made if a player suffers a head injury, even if all replacements have already been used.
To avoid potential abuse of the rule, opposition teams will also be able to make a change at the same time.
However, Premier League clubs have voted against the use of five substitutes for a third time, despite Ifab's confirming an extension to the rule on Wednesday.
Instead, the number of top-flight players allowed on the bench has increased from seven to nine.