IU dont want to put a downer on you with regard to the question,but although my own opinion is that if you are competent then that should suffice
The church may have guidance which excludes you as a domestic installer
I am not able to give a link or precise wording,but the churches governing body I think its the ecclisiastical council or other issued guidance which I have read fairly recently
They wrote a memorandum of guidance to the churches stating that they were to be aware of who they engage for electrical work.It then went on about DI is for domestic work only and that an approved contractor should be engaged to carry out work on churches
My advise would be to carry out the work,issue the correct certification and what may be may be
But good luck anyway