Where to store data import logic

I have a question regarding best practices:

We import a lot of data (basically game rules) from .csv/JSON in data structs/tables. However, there are some calculations/conversions going on before it ends up in a clean format to be used by the game mode for game logic. Where should we store these calculations/conversions and data arrays? We now have everything done in the game mode as separate functions which kinda pollutes the game mode and I don’t think the game mode should handle data import and conversion. Should we just create a blueprint that handles all of this and provides the clean data to the game mode (filling up the arrays in the game mode) when finished or is there another place that is better suited?

Hi, anyone who wants to share their own experiences or suggestions?