Were surname upgrades a well known practice in the Spanish Empire?

Question

People everywhere have names, and some seek to change their name. Spanish speaking people in particular generally have two surnames, paternal and maternal, in that order. Whether the maternal one appears at all depends on formality, context, and preference.

In an era before government IDs and databases, someone whose maternal surname was not well known could quietly adopt and start to use another. Who would stop them? I have one example here of a man in New Spain around 1800 who seemingly never used his mother's surname (Fonseca), then in middle age began to use a grander looking one (de San Vicente). There may be other explanations for the change but I am inclined to read it as an attempt at social climbing. In any case, was adopting a fictitious second surname a documented practice in the Spanish empire?

Answer 1

This is more a long comment than an answer.

There are two questions here, one related to the upgrade and another related to the fictitious surnames.

About the upgrade. There are several surnames that are a combination of both family names, where the second one is the one that carries the tradition (Ruiz Tagle, Pérez Cotapos, García Huidobro), in those cases the second surname is important, while the first one is quite common. So, by using a combination you can create a new surname that preserves the lineage. You can even find people with four surnames, because both family names are combined, for example, a name could be something like "María de los Ángeles Pérez Cotapos García Huidobro", this is not a joke, it might happen. In some cases, the second name of a person might be a surname.

Since people from aristocracy is well versed in the genealogy of their kind, is quite difficult to change your surnames in order to get an upgrade to reach them, because aristocrats know quite well who belongs to them.
An example of the importance that aristocracy gives to their genealogy, you can find webpages like this, where some combined surnames already existed on XVI century. Guessing, I will say that less than 0.3% of people has combined surnames. All of them belong to the upper social class. An example of combination starts with family Garcia Huidobro on 1697.

Since often people did not have a known father, it was common to double the family name from the mother (González González) or even use both family names from the mother. Only when your father recognized his children, they had the right to use his family name.

An interesting example is Bernardo O'Higgins (link in spanish), bastard son of the Viceroy of Peru (Ambrosio O'Higgins), who did not give his surname to his son, hence he was known as Bernardo Riquelme, where Riquelme was his mother surname. Only when he demanded his dad in the court he got the right to use his father surname.

Only people from aristocracy is interested in their family names, poor people does not pay too much attention to their lineage. Actually, poor people often use alias instead of surnames, hence, fiction comes to the name, not for the surname.
I do not have evidence of fictitious surnames.