Q. 1. What is the position of the Catholic Church regarding Catholics attending the Ash Wednesday ceremony at a Protestant Church?
A. 1. While you cannot substitute the Catholic Mass for a Protestant service, you can attend a Protestant Ash Wednesday service without the fear of committing a sin.
Ashes are a Sacramental. As such, they do not have the same conditions as the Eucharist.
It is not uncommon for Catholics who are involved in mix marriages to alternate which Church they attend for the Ash Wednesday ceremony.