If I modify the english language translation in messages.ini is it overwritten on upgrade?

Mautic 3.3.3

I’m thinking of modifying some of the labels and such to make it more meaningful to the intended audience. Can I just modify the existing messages.ini files that are in each ‘bundle/Transaltion/en_US’ folder? Will they be overwritten if I upgrade.

Or should I try to make a custom language file and then choose that from the language dropdown in the UI?

Thanks!