Did the Scribes change the text of the Bible?

Bible corruption

The Mechilta (Beshalach, Shirah ch. 6 on Exodus 15:7) lists eleven places in which the Biblical text used a euphemism (kinah hakatuv). For example, it says in Zechariah (2:12) "Whoever touches you, touches the apple of his eye." It should have said "touches the apple of My [i.e. G-d's] eye." However, out of respect for G-d, the text used a euphemism instead. There is no reason to believe that someone later changed the text of the Bible. Rather, the original text itself was written with a euphemism.
In Shemot Rabbah (13:1) we find that R' Yehoshua ben Levi quoted this same example from Zechariah but, rather than calling it a euphemism, he called it a "correction of the Scribes" (tikkun Sofrim). Similarly, in Bereshit Rabbah (49:7) we find his student, R' Shimon, giving the same explanation to the verse (Genesis 18:22), "And Abraham was still standing before G-d." R' Shimon says that really G-d was waiting for Abraham but, out of respect for G-d, there was a "correction of the Scribes." This explanation of R' Shimon is quoted by Rashi on that verse.
The question that remains is whether tikkun Sofrim means that scribes actually changed the wording of the Bible or is it really the same as a text using a euphemism (kinah hakatuv) but that the Scribes discovered and explained this euphemism? In other words, the Scribes fixed the understanding of the verse. Do R' Yehoshua ben Levi and R' Shimon agree or disagree with the Mechilta?
There is no reason to assume that they disagree. Indeed, the Rashba (quoted by R' Eliyahu Mizrachi on Genesis 18:22) explains that they do not disagree and that the change the Scribes made was to the understanding of the text. That is how they fixed the verse. Maharal (Gur Aryeh, there) agrees. R' Yosef Albo writes a little differently in his Sefer HaIkkarim (3:22):

The meaning is not that any person changed anything in the Torah, G-d forbid, because no one would forge a book and then say "I forged this" or "I changed this." How could they say that the Scribes changed it? Rather, the meaning is that... [the Torah spoke] like a scribe who changes his words out of respect for G-d."

While some editions of Rashi (on Genesis 18:22) have him actually saying that the rabbis changed the text, manuscripts do not bear out this reading. It must have been added by a copyist who made a mistake. See the Berliner and Mossad HaRav Kook editions of Rashi and the Yefeh Toar on Bereshit Rabbah 49:7. Indeed, had earlier scholars known this they would not have been so confused on this issue. For example, see R' Avraham Bucrat's Sefer Zikaron on Rashi where he argues that Rashi believes that tikkun Sofrim means the same as kinah hakatuv but then stumbles over Rashi's language. However, we have found proof that Rashi understand tikkun Sofrim like the Rashba that it means that the Scribes fixed the meaning of the text. On Job (32:3) Rashi writes, "This is one of the verses in which the Scribes fixed the language of the text. It should have read, 'And they condemned G-d in their silence' but the text used a euphemism (kinah hakatuv)." Here we see clearly Rashi saying both that the text used a euphemism and that the Scribes fixed the language. Obviously, the Scribes fixed the language by explaining the text's true meaning without the euphemism. See also Rashi's commentary to Numbers 11:15. Ibn Ezra, at the end of his introduction to his commentary on the Torah, rejects the entire concept of tikkun Sofrim. See also his commentary to Numbers 11:15 and 12:12.
However, it should be noted that the Tanchuma (Beshalach 16) as we have it says that the Scribes actually changed the text of the Bible. No less than R' Azariah de Rossi, who was called a heretic by the Maharal and whose books were banned, testified that two manuscripts of Tanchuma in his possession did not have this passage (Me'or Einayim ch. 19). Only one rishon, the Aruch (s.v. Kabed, 1) quotes this tradition of the Tanchuma. While the Aruch believed that the Scribes did, on limited occasions, change a letter in the Torah - with the exception of Genesis 18:22, every case was the change of one letter - the overwhelming majority, as we have seen, did not believe this. The manuscript evidence has proven that the Aruch was himself, ironically, relying on a faulty text of the Tanchuma. (See also Responsa Radbaz no. 1020, vol. 3 no. 594 who poses many difficult questions to the Aruch).

Regarding words that are written one way but are read another way (kri uktiv) etc., Radak in his introduction to Joshua claims that these were due to different texts of the Bible. For this, he was sharply criticized by R' Yitzchak Abarbanel in his introduction to Jeremiah. Abarbanel write, "A scroll which has one letter missing is invalid. How much more so that many letters would be missing." Therefore, Abarbanel suggests that the reading (kri) was added by Ezra as an explanation to the writing (ktiv). However, this too was criticized by later scholars.
The simple and most obvious explanation for kri and ktiv is that offered by the Maharal (Tiferet Yisrael ch. 66) and Radbaz (Responsum no. 1020, vol. 3 no. 594). The prophets who wrote their books included both kri and ktiv in them. Since, as some suggest, these books were revealed to Moshe at Sinai and then later to the prophets to say and write down, the kri and ktiv originate at Sinai. What this means is that the books were originally written with the kri and ktiv. In addition to this, Malbim in his introduction to Jeremiah boldly claims that the ktiv represents the simple meaning - the pshat - and the kri represents the exegetical meaning - the drash. Malbim follows through with this in his commentary and demonstrates this difference between pshat and drash. One who truly wishes to understand the Bible would do well to study it with the commentary of Malbim.