First, a word about the Maccabean Hypothesis. The fact that the first part of the book may be by a different author than the apocalyptic sections does not mean that the first part was compiled "a few hundred years earlier." An introduction to Daniel published by the US Council of Catholic Bishops states:
This [entire] work was composed during the bitter persecution carried on by Antiochus IV Epiphanes (167–164 B.C.) and was written to strengthen and comfort the Jewish people in their ordeal... The book contains traditional stories (chaps. 1–6), which tell of the
trials and triumphs of the wise Daniel and his three companions. The
moral is that people of faith can resist temptation and conquer
adversity. The stories bristle with historical problems and have the
character of historical novels rather than factual records. What is
more important than the question of historicity, and closer to the
intention of the author, is the fact that persecuted Jews of the
second century B.C. would quickly see the application of these stories
to their own plight.
As to the question of why the author believed his writing would be accepted, we need look no farther than other biblical books which modern scholars believe to have been published under a pseudonym. According to the Documentary Hypothesis, Moses is not the true author of the Pentateuch. Such scholars believe that Deuteronomy in particular was written in the time of King Josiah and successfully promoted by the high priest Hilkiah as having been the final revelation to Moses. The USCCB site cited above says of Deuteronomy:
The book was probably composed over the course of three centuries,
from the eighth century to the exile and beyond. It bears some
relation to “the Book of the Law” discovered in the Jerusalem Temple
around 622 B.C. during the reign of King Josiah (2 Kgs 22:8–13)...
Over the book looms the disaster of 722/721, the fall of the Northern
Kingdom, Israel. The detailed description of siege (28:49–57)
especially echoes the fate the North suffered at the hands of the
So we may speculate that just as the author/s of Deuteronomy believed they could publish that part of the Torah in Moses' name, so the author/s of the Book of Daniel did in Daniel's name. A similar principle was at work in the case of 1 Enoch, which was never accepted as canonical but which was paraphrased as a real prophecy of the historical Enoch in the Letter of Jude:
It was of these also that Enoch in the seventh generation from Adam
prophesied, saying, “Behold, the Lord came with his holy myriads, 15
to execute judgment on all, and to convict all the ungodly of all
their deeds of ungodliness which they have committed in such an
ungodly way, and of all the harsh things which ungodly sinners have
spoken against him.” (Jude 1:14-15)
The OP says "I thus presume such a person must have been a person of considerable authority within the Jewish community." This fact is not certain but in any case we can again point the the Book of Deuteronomy, which was "found" in the Temple, promoted by the high priest and confirmed by the prophetess Hulda. (2 Kings 22).
Assuming that pious forgeries, including the Book of Daniel, indeed made their way into the Holy Scriptures, we can only speculate as to the reasons that their authors believed they would be accepted. Here are two overlapping possibilities that present themselves regarding the author of the Book of Daniel:
He may have believed that there were precedents for such writing, especially Book of Enoch, important parts of which were already in circulation at the time Daniel was written if the Maccabean Hypothesis is correct.
He may have believed that God inspired his writing. A parallel is found in the Book of Revelation where the NT prophet John believed that Jesus had dictated messages to the 7 churches through him order to encourage Christians to resist Roman persecution.