Apple made a lot of visual changes in release 10.10 (“Yosemite”) of Mac OS/X. One of the most obvious was to change the system font, as used throughout the desktop, from Lucida to Helvetica.

A lot of people love Helvetica, so presumably they were happy. Others were less satisfied, leading to a little rush of code and articles to help you switch the system font back to Lucida or to some other font that happens to appeal.

But these people are missing the point. The substitution you want to make is not to your own desktop, but to that of your most type-conscious Mac-using Helveticaphile friend. And it is to switch the system font from Helvetica to Arial.

Delightfully, you can do this without needing admin privileges—no password required, all you need is to get control of their keyboard for a couple of minutes.

Here’s how:

1. On your own machine, provided you are also using a Mac, install Yosemite System Font Patcher and its dependencies following the instructions in its README:

$ git clone https://github.com/dtinth/YosemiteSystemFontPatcher
$ brew install fontforge --with-python

2. Retrieve and patch the Arial font files so they report themselves as system fonts:

$ cd YosemiteSystemFontPatcher
$ cp '/Library/Fonts/Arial.ttf' '/Library/Fonts/Arial Bold.ttf' .
$ bin/patch 'System Font Regular' 'Arial.ttf'
$ bin/patch 'System Font Bold' 'Arial Bold.ttf'

3. The above should have created two new font files, in the current directory, called System Arial.ttf and System Arial Bold.ttf. Make these available somewhere you can easily retrieve them on your friend’s machine (shared in the cloud or whatnot).

4. On your friend’s machine, when you see the opportunity, retrieve the System Arial.ttf and System Arial Bold.ttf files and copy them into the $HOME/Library/Fonts directory. You must be logged in as your friend to do this, as it must be their home directory whose font library you are copying into.

And you’re done. The change will only take effect for apps started after the fonts have been installed, or globally from the next login—if you want to make it happen immediately, I’m afraid you’ll have to log your friend out.

Now, see how long it takes them to notice. For best effect, engage them in conversation about how clean and elegant Helvetica is, with reference to their own desktop.