Can a Catholic cite a religion as a reason for not doing something even if that thing isn't officially prohibited by the Church?

So my impetus for this question is covid-19 vaccines, but it could be about anything from face masks to filling out the census. If the Catholic Church doesn't officially say something is wrong, is it licit for an individual adherent of the Catholic church to exempt himself or his family from that thing using religion as the basis for that exemption? For instance, Quakers claim a religious exemption from wars on the grounds that their religion is pacifist. Now, I know Catholics have also claimed this religious exception (e.g. Dorthy Day, Daniel Berrigan), but I also know that the Church has Just War doctrine and the magisterial teaching of the Church did not explicitly forbid Catholics from participating in any wars protested in the last century. So, would these objectors been right (in the eyes of the Church) in calling their objections religious objections or were their objections merely a matter of personal conscience?