THE EUANGELION BLOG: Pseudepigraphy as a Non-Deceptive Fiction (Michael F. Bird). Let me introduce a couple of notes of caution here. First, Salvian's justification of the forged writing as "a completely transparent and therefore non-deceptive fiction" could also be taken as an after-the-fact justification once the forgery was detected. I am not at all sure that we should take this as a good example of pseudepigraphy done in good faith with no intention to deceive.
Second, contrary to the impression given by the quotation from Baum, Salvian does not actually confess to the forgery. He presents his justifications as speculations about what the forger might have been thinking and always refers to the forger in the third person. You can read an old translation of the full text of his Letter 9 here, posted by Roger Pearse. Pearse also has additional comments here on Bart Ehrman's use of the text.
The broader issue, of course, is whether such impersonations were constructed in such a way as to be obviously fictional, in which case there would have been no intent to deceive. It is not at all obvious to me that biblical pseudepigrapha such as the Pastoral Epistles or the Book of Daniel, or other pseudepigrapha such as the books in 1 Enoch, would come under this category. Some of the other Old Testament pseudepigrapha might.
That is not to say that all ancient biblical pseudepigrapha were exactly forgeries intended to deceive. I have explored some of the psychological complexities of this issue in my 2006 SBL paper, especially toward the end: Scripture as Prophetically Revealed Writings. And my 2012 SBL paper also deals with some similar issues: The 94 Books of Ezra and the Angelic Revelations of John Dee.