Exploring the Scripturesque: Jewish Texts and Their Christian Contexts (2009)
By Robert A. Kraft

Although rabbinic Jewish sources also comment about changes being introduced into Greek scriptures, the complaint is not specifically against Christians, and the alleged changes are not characteristically Christian in flavor. A relatively late tractate, partly supported by both Palestinian and Babylonian Talmuds, gives two variant reports about translations of Torah into Greek under king Ptolemy and then lists “thirteen” (actually fourteen) passages allegedly “altered” in the Greek by the original translators. 210 The listed changes are relatively minor matters, but in at least two passages, the direction of the supposed change runs counter to traditional Christian interests (and the preserved LXX text!) regarding plurality in the Godhead. The Jewish sources complain that Gen 1.26 “Let us make man” has been changed to “I will make man,” and Gen 11.7 “Let us go down” to “Let me go down.” Both passages, with the accepted Hebrew (and LXX) plural designations, played a positive role in Christian apologetics
While Kraft also has a section on the earlier day about the Christian charges of interpolations, some by Justin Martyr, his discussion of the Romans-Psalms situation on p. 76-77 is quite weak, not wanting to give Paul credit for the beautiful pastiche.

Thackeray reference to be checked out p. 89-95

The Letter of Aristeas: Translated with an Appendix of Ancient Evidence of the Origin of the Septuagint (1914)
Henry St. John Thackery (1869-1930)

God put counsel into the heart of every one of them, that they were all of one mind, and they wrote out for him the Law by itself.3 But they altered thirteen4 passages in it, and they are these:5— p. 91-93
We should keep in mind that the "LXX" is unreliable on various angles, this just documents the fact that the Jews specifically said that they tampered with some passages.

This is also Thackeray, but a bit different, just as a research FYI

And this is Thackeray on Romans-Psalms (check sister page)

Messianic_Apologetic article

However, the quote partially is found here:

However, I can not find the part about "altering", but it is in Thackeray.

Messiah Truth article