UEFA announced a number of changes.
The official website of UEFA reports that starting next season the teams will be able to hold the fourth substitution in extra time.
This practice is now used at the World Championships.
Also, any electronic devices can be used for the coaching staff and medical personnel. For example, doctors can immediately use the laptop to determine if the player has a concussion.
This will apply to all matches held under the auspices of UEFA, starting with the season-2018/19.