How to make the GNOME Shell Activities Bar small all the time

The ArchWiki is a very good source of information. This is where I found the following:

To configure the GDM theme use this command:

sudo -u gdm dbus-launch gnome-appearance-properties

For more configuration options, use this command:

sudo -u gdm dbus-launch gconf-editor

And modify the following hierarchies:

/apps/gdm/simple-greeter
/desktop/gnome/interface
/desktop/gnome/background

You may end up with an Xauth error. If that happens, try gksudo instead of sudo. If the error persists, you can do this:

xauth list $DISPLAY

This gives you the xauth cookie being used by your user. Copy the output, then run the following, replacing "" with the output of the previous command.

sudo su -u gdm
xauth add <cookie>
dbus-launch gnome-appearance-properties

This logs you in as the gdm user, adds the cookie, permitting gdm to use your display, and launches gnome-appearance-properties.

While this isn't the best solution, I get around the problem of low resolution icons by just pointing directly to the highest possible version inside the .desktop file. In this case specifically, I have it pointing to a local copy of the official 256px icon, but any location should work.

Icon=/home/patrick/.icons/sublime-256.png