Derby will be permitted to bolster their squad by signing out-of-contract players following a ruling by the English Football League.
The Championship club are currently subject to a transfer embargo, meaning they cannot sign players from other clubs on permanent deals or pay loan fees.
They are also limited to a maximum of 23 players of "professional standing" in their squad.
Derby were deemed to have reached this 23-man limit by the EFL, a ruling which also therefore prevented them signing out-of-contract players.
The club contested this, however, arguing that the players who featured in last season's Covid-hit FA Cup tie at non-League Chorley should not be classified in this way.
Ordinarily, a player of "professional standing" is someone who has featured in a first-team match in the league, FA Cup or League Cup.
Derby were forced to field a side made up almost entirely of academy youngsters at Chorley after their entire first-team squad, including manager Wayne Rooney, were asked to self-isolate.
The club claimed this classification of academy players was unfair and, following a review, the EFL has now granted an exemption on this matter.
An EFL statement read: "Further to a request from Derby County, the EFL board has now considered the circumstances regarding appearances made by a number of academy players in the FA Cup tie against Chorley earlier this year.
"Upon review, the board has determined that the appearance in that fixture by those players will not be considered as part of any assessment of whether they are players of 'professional standing' in line with the League's embargo policy, due to the exceptional circumstances that applied at the time of the fixture."
This means Derby could now consider offering deals to free agents such as Ravel Morrison and Phil Jagielka, who have been training with the club.
The EFL dismissed requests from Derby to have other aspects of the embargo relaxed.
The statement added: "The board rejected a further request to relax an enhanced embargo that remains in place in respect of other regulation breaches.
"The club will therefore continue to be under wage restrictions on player recruitment and limited to a squad size up to 23 players of 'professional standing'."
