Former All-Ireland winning manager Pete McGrath will take charge of Rostrevor next year but Paul McIver has ended his spell in charge of Kilcoo.
The managerial changes were announced separately by the two clubs on Tuesday.
McGrath, who resigned as Louth boss in July, will manage his hometown club for the first time in what will be their centenary year.
McIver has ended his four-year term as Kilcoo manager following their county final defeat by Burren.
The three-point loss to Burren at Pairc Esler denied Kilcoo a record seventh consecutive Down SFC title, with McIver in charge for three of those championship victories.
The Eoghan Rua club also made it to the 2016 Ulster club SFC final under McIver, where they lost to Slaughtneil.
In a statement, the Kilcoo club thanked McIver and his management team for their "commitment and dedication" and for the "joy and success" they had brought to the club.
"Paul took on the management of our senior team in late 2014 and took us to three county titles, culminating in a remarkable six-in-a-row in 2017," the statement added.
"We can't thank him and his assistants enough for the work they have done. We wish each and everyone of them all the best in the future."
McGrath, who led Down to All-Ireland successes in 1991 and 1994, will return to club management after spells in charge of the Down minors as well as the Fermanagh and Louth senior teams.
The appointment of the 65-year-old, who was part of the first Rostrevor team to win the Down SFC in 1976, was ratified by the management committee of the St Bronagh's club.
Rostrevor won promotion back to the senior championship last year but were knocked out in the first round by Warrenpoint.