From: Rabbi Moshe Sofer
To: Rabbi Yaakov Weiler
The Chasam Sofer rules that an erroneous parshah break renders the Sefer Torah invalid but is correctable since no Divine Name is involved. Regarding an erroneously written suffix to a Divine Name, he distinguishes three cases: a correctly written suffix may not be scraped (horadah mikedushah); an erroneous suffix may not be fully erased; but scraping an erroneous suffix is fully permitted, as the prohibition is at most rabbinic, the suffix was never truly sanctified, and leaving the error degrades the entire sheet.
Source: Shu"t Chasam Sofer YD §260