There you go again, cutting and pasting. I could do the same, but won't. For instance, there's a whole piece on excommunications in the Catholic Encyclopedia--particularly on the moral nullity of an unjust excommunication. Bishops are not infallible--or is that news to you? They sometimes unjustly excommunicate--Bruskewitz, in particular, is excommunication-happy.
Excommunication is said to be unjust when, though valid, it is wrongfully applied to a person really innocent but believed to be guilty. Here, of course, it is not a question of excommunication latæ sententiæ and in foro interno, but only of one imposed or declared by judicial sentence ... a person unjustly excommunicated is in the same state as the justly excommunicated sinner who has repented and recovered the grace of God; he has not forfeited internal communion with the Church, and God can bestow upon him all necessary spiritual help. However, while seeking to prove his innocence, the censured person is meanwhile bound to obey legitimate authority and to behave as one under the ban of excommunication, until he is rehabilitated or absolved.
Thomas says the same:
If, however, he were to contemn the sentence, he would "ipso facto" sin mortally. (Sup q. 21 a. 4)