Create the following file: /etc/vim/vimrc.local
" This file loads the default vim options at the beginning and prevents
" that they are being loaded again later. All other options that will be set,
" are added, or overwrite the default settings. Add as many options as you
" whish at the end of this file.
" Load the defaults
source /usr/share/vim/vim80/defaults.vim
" Prevent the defaults from being loaded again later, if the user doesn't
" have a local vimrc (~/.vimrc)
let skip_defaults_vim = 1
" Set more options (overwrites settings from /usr/share/vim/vim80/defaults.vim)
" Add as many options as you whish
" Set the mouse mode to 'r'
if has('mouse')
set mouse=r
endif