The Masoretic text is of the middle ages, of much later origin than the Septuagint and the pre-Masoretic Hebrew OT of the Dead Sea Scrolls.
I was under the impression that the MT was done in the 7th century...I could be wrong though.
By comparing the Masoritic text with a more ancient Hebrew text, one could tell if the unbelieving Jews have changed their Scriptures since the time of their rejection of Christ.
First of all, I would be surprised if the Jews did not change their Scriptures IN GENERAL. Scriptures are a fluid thing, especially in regard to the Hebrew Scriptures after Christ.
Second, who are the "unbelieving Jews" and what is their Scripture?
Third, your original question stated the idea that there is a possibility of the minimizing of the prophesy of His Comming, due to perversion of the Scriptures. How does your entire response above enlighten that question/dialogue?
Fourth, I am not of the opinion that the changes of the MT created a barier for the belief in Christ as the Messiah. Christ as Messiah in the OT has been "proven" so whether or not the MT has perverted anything is slightly moot because Christ is in the OT no matter what the historical changes of the MT are.
Maybe i'm misunderstanding your questions and posts as a whole...Any help you can provide me, in terms of clarity, would be great!