Teams will be allowed to use replacement players in County Championship cricket this year to cover illness and significant life events, as well as injuries.
In a season-long trial, a player can be fully replaced with a like-for-like cricketer if the need arises, rather than just have someone emerge as a substitute fielder.
The 'significant life events' element includes attending children's births and family bereavements, with these absences needing to be approved by the CEOs of both counties competing in a particular match.
Replacement players will only be permitted in the Championship, not white-ball games.
There will be an eight-day stand-down period for any player withdrawn from a game due to illness or injury, which should help eliminate any danger of rule-bending.
Any injury or illness switches would need to be cleared by the relevant counties' chief medical officers.
The issue of replacement players reared again last summer when England all-rounder Chris Woakes dislocated his shoulder fielding on the boundary against India at The Kia Oval and then had to bat with one arm in a sling towards the end of the game.
Earlier in the series, India's Rishabh Pant batted in considerable pain after his foot was fractured mid-game.
There have already been trials in Australia, Indian and South African domestic cricket, although they did not include provisions for illness or significant life events.
ECB head of cricket operations Alan Fordham said: "This is all about getting the best-quality cricket, looking after players and not having players playing in games where they shouldn't be.
"If teams are going to start pushing right at the edges of the regulation, then it risks a chance that we'll have to backpedal from some of the things we are putting in place."
The ECB expects injury replacements to be used in 25 per cent of County Championship matches.
The first round of games begins on Good Friday.
In other county news, former England international Ravi Bopara has retired from English domestic cricket after opting not to play in this season's Vitality Blast in order to focus on commentating.
The 40-year-old - who is considering applying to become England men's new national selector following the departure of Luke Wright - has featured in every season of the T20 competition since its launch in 2003.
Last term, he scored over 450 runs for Northamptonshire in their run to the final, including a match-winning 105 not out from 46 balls in the quarter-final victory over Surrey at The Kia Oval.
Bopara, who has also played county cricket for Essex and Sussex, told ESPNcricinfo: "I did think hard about the Blast. But I'm excited for new things. I've had a good opportunity with commentary, which I think I'd be silly to turn down."
The all-rounder is currently head coach of Karachi Kings in the Pakistan Super League.
