BneiAvrom

“One should avoid tearing or breaking a letter while tearing open a package do to the violation of the melachah of mocheik, erasing, according to one view in the poskim. Where it is impossible to access the food otherwise, one way rely on a lenient view and tear letters while opening a package. This should preferably be done in an irregular manner, for example, with the left hand”. From the safer “Halachos of Opening Packages on Shabbos”, Chapter 6. [By Rabbi Menachem M. Abramson]. He discusses the dagul meravava and others in the footnotes.