I was told many poskim including R. Moshe permit cutting through letters in a destructive manner for the purpose of getting food.
Where is the teshuva by Rav Moshe found? Who are the others that agree with this?
The prohibition applies only if a significant part of the letter or picture will be broken. If, however, the basic form and shape of the letter or picture remains intact, Erasing did not take place
Halachipedia (here) writes the Ashkenazi custom is to forbid cutting lettering on food packages, while Sefaradi poskim permit it (see Yalkut Yosef Shabbat vol 5, p. 117 who permits tearing through letters because it is a psik reisha d’lo nicha lei on a rabbinic prohibition).
This being said, I see R Eliezer Melamed (PH Shabbat 18:3) permits if there is no other way
Others maintain that one may open such a package, since all parts of the letters actually remain, but have simply been separated from each other (based on Rema). Le-khatĥila it is proper to be stringent, but when there is no way to open a package without tearing letters, one may be lenient. One who opens the package has no interest in “erasing” the letters, and the action is not constructive but destructive.