Does this din also apply by a Mezuzah? By a Sefer Torah the problem is since it is read b'tzibbur, but by a Mezuzah no one will see it.
The shailo came up like this. A Bachur learned how to be a Sofer and even has a csav kabbalah already. His father wants him to write for him mezuzos however this bachur doesn't want to write any Shemos so he will get someone else to write the shemos (c'sidran obviously.) But with someone else's csav you could run into the problem of menumar. The shailo is if it's even noge'ah by a mezuzah at all.