Change the permissions of the files generated by WordPress on the server

I always upload my WordPress files on the server so the “owner” is my username and I can change the permission to, let’s say, 770. But when I install a plugin, the owner becomes “www-data” and the permission is rw-r-xr–. However, I need to modify some files. Can I do something in the WordPress config to change the generated file’s default permissions? I’m not the server’s root. Thank you.