Rooney has been part of an interim coaching quartet alongside Liam Rosenior, Shay Given and Justin Walker since Philip Cocu was sacked earlier this month.
But after the arrival of ex-England boss Steven McLaren as technical director this week, changes have been made with Derby winless in their last nine matches and on a run of four straight defeats.
Rooney's new role will see the 35-year-old, contracted as a player-coach, scale back his playing role significantly, suggesting his career on the pitch is nearing an end.
The former Manchester United forward will take responsibility for the team selection and tactics this weekend.
Rooney remains a candidate to get the job full-time, but no decision will be made before the outcome of a proposed takeover led by Sheikh Khaled bin Zayed Al Nehayan.
Rooney made clear earlier this month he would be interested in the role if it were to be offered to him. He is yet to gain his full set of coaching badges but is making progress on gaining his A licence.
Derby host Wycombe, who sit third from bottom, at Pride Park on Saturday before fellow strugglers Coventry visit on Tuesday.
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