I think the OP is saying that the Bishop has given permission for the non-catholic individual to have a Catholic funeral. I don’t think they were saying the Bishop has given permission for the spreading of ashes. Of course, I could be compeltely wrong, so hopefully the OP will clarify.
In answer to the question, I do not believe that it is an acceptable practice to divide the ashes of an individual; however, I cannot find a specific prohibition among the Liturgical Norms on Cremation
ewtn.com/library/CURIA/CDWCREMA.HTM . The Liturgical norms do say we need to treat the cremated remains **the same as we would a body. **I don’t think we would usually “divide” a person’s body to be buried in two different places; however, the Church has done exactly this with some relics…so I am totally at a loss on this one