Offer extension = Protract
Pro = for
tract is a psalm sung as an anthem during Lent ( R.C. )
To be printed means ( wrote he hopefully ) how the answer should be written.
Must admit I didn't like this clue when I did the crossword this morning -- and still don't. It is the only word which I can find which will fit the pattern *r*t*a*t. The definition part is fine but I feel the clue would have lost nothing had it ended at anthem.