@CTBcin,
I have never gone to Rouen, despite living in the region.
It’s status is a bit confusing for me
According to my search, the St Ouen ex abbey
is own by the city of Rouen. And it
is assigned to the Diocese of Rouen. (1)
It is conformed to the French law and the situation of the majority of churches building in the country.
The churches who are built before 1905 are usually the property of the civil administration such as the “commune” (city) and the Cethedrals to the French State.
The fact that it is assigned (
affecté) to the diocese means it is assigned/consecrated (
affecté) to the cult. That’s means it is not deconsecrated and the Catholic worship can happened there.
For the material needs, the secular administration pay for the building repair and the Church pays for the heating and the usual maintenance. In the case of this ex-abbey I don’t know if it is the same because of the secular nature of almost its use.
This church is also classsified as an Historic Monument by the French State. It gives its a protection against destruction and strict restauration norms and the State give money for the maintenance of the building.
Apparently, you are right, no regular worship seems to happened. According to a 2014 article of this militant website, a mass is celebrated once every 6 months so that the Church remains assigned to the diocese. (2) The main usage is completely secular exhibitions and concert.
The diocese of Rouen website give the name of a lay administrator (as opposed to a pastor). (3)
1:
https://www.patrimoine-religieux.fr...6540-Rouen/175828-AncienneabbatialeSaint-Ouen
2:
Mgr Descubes veut-il liquider l'abbatiale de Rouen ? - Riposte-catholique
3:
Abbatiale Saint-Ouen - Diocèse de Rouen
I sent a message to a friend linked to Rouen to have a confirmation of all above. Do you have another question?