Roughly how much processing power is needed to loop through string-Lists/Arrays when loading/saving stored data?

I recently learned how to store data using a very basic BinaryFormatter/FileStream method that saves the game data in string list.

Each string is about 10 characters long, I am planning to use about 10-20 string-lists, all of them will have about 50 elements, and they might on some occasions be multiple saves and loads of these lists every minute.

Since I have a very basic understanding of how to store information, my only method of saving a file is to completely overwrite the previous save file even if only a single element is to be changed.

This is obviously not optimal, but I want to keep it as simple as possible since this is my first project. Also I speculate that the processing power described here should be pretty limited since these are after all only string lists (and no large png:s for example).

So the question is: Is it a correct assumption that the processing power required for this is relatively small? Or will it cause major lags if Unity is forced to Load, loop through and save these string-lists multiple times per minute?