A thread in the German Genealogy group on Facebook suggested the feminine -in suffix (or masculine suffix of -er) was a common social convention for southern German surnames. And they referred to this affix difference as a ‘diminutive’. (Is that the right label?)
How would such a surname change be recorded in Gramps?
As an alternative name of a different type? Probably not, if that was the surname used from birth? As a “Diminutive” Origin in the name definition?
It is related to the Patronymic or Matronymic but rather than indicating the name is derrived from the given name and gender of a parent, it is a gender-bent patrilineal.
I don’t have access to that thread but I have seen the -in suffix in church records from the 1800s for my ancestors in Baden. For simplicity, I chose to ignore it for purposes of data entry in Gramps. But (inconsistently on my part) I did choose to record some of my cousin’s female Polish ancestors’ surnames with the -ska suffix rather than -ski.
I’m glad Gramps gives users the flexibility to do whatever works best for them. I generally don’t do much with alternative surnames except when they change due to adoption. I do use the surname grouping feature.
The female suffix is also common in Austrian church records, but I think most people/genealogists just record the name without the suffix. It’s a common social convention, but the suffix has no additional information.