Football law-makers have approved FIFA's plan to let teams make up to five substitutions in a match, while VAR could be temporarily dropped by leagues.
It will be at the discretion of each competition whether new guidance is implemented.
FIFA proposed the change from three substitutions to five as a move to protect player welfare in the coronavirus era as football slowly returns to normal.
The International Football Association Board (IFAB) gave its nod of approval, but the new law will be applicable only in competitions scheduled to finish by the end of 2020.
VAR could also be temporarily cut, with football re-emerging at a difficult time when it may not always be possible to implement the same technology as before COVID-19 took hold.
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IFAB said in a statement on Friday: "For competitions which have either started or are intended to start, but are scheduled to be completed by December 31, 2020, the IFAB has approved FIFA's proposal to introduce a temporary amendment to Law 3 – The Players, which will allow for a maximum of five substitutes to be made per team.
"However, to avoid disruption to the game, each team will only have three opportunities to make substitutions; substitutions may also be made at half-time.
"The temporary amendment comes into force with immediate effect, and has been made as matches may be played in a condensed period in different weather conditions, both of which could have impacts on player welfare.
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"The decision on whether to apply this temporary amendment will remain at the discretion of each individual competition organiser, while the IFAB and FIFA will determine at a later stage whether this temporary amendment would need to be extended further (e.g. for competitions due to be completed in 2021)."
The IFAB statement added: "In relation to competitions in which the video assistant referee (VAR) system is implemented, these competitions are permitted to cease its use upon restart at the discretion of each individual competition organiser.
"However, where VAR is used, all aspects of the Laws of the Game and, by extension, the VAR protocol will remain in place."
