At the moment this behaviour is hard-coded. Once the file becomes more than 3 months old, the app starts prompting whether you want to update it.
The easiest solution in this case is to set the database file's date to the current date, which will suppress the prompts for another 3 months.
This can be done by using a third-party file manager to assign the current date to
oui.txt or run in a command prompt:
copy /b oui.txt +,,