The measure would be allowed during extra-time, starting with the under 19 European Championship in Germany in July and the European under-21 contest next year in Poland.
A UEFA statement said the executive committee had "agreed to allow the testing of a fourth substitution in extra time" at a series of tournaments.
These will be at the European under 19 Championships in Germany and next year in Georgia, the European under 21 Championship finals next year, the womenâs European Championships this year in Slovakia and in 2017 in Northern Ireland.