Jan Štětina

Includes custom HTML/CSS/JS code in the section on every blog in the network.
Very simple, but sometimes useful plugin.
After activation visit Network Admin –> Settings –> Multisite wp_head Code for setup. Nothing else is needed.
Developed for private use, but has perspective for more extensive usage. I can’t guarantee any support in the future nor further development, but it is to be expected. Kindly inform me about bugs, if you find any, or propose new features: <a href="mailto:zaantar@zaantar.eu?subject=[multisite-wphead-code]" rel="nofollow ugc">zaantar@zaantar.eu</a>.

Multisite wp_head Code

Includes custom HTML/CSS/JS code in the  section on every blog in the network.

Gaiaz Iusipov

Simplest plugin that injects any code into wp_head().

Header Code

Simplest plugin that injects any code into wp_head().

Multisite wp_head Code vs Header Code