wpler

<a href="https://www.wpler.com/linkmanager-fur-multisites/" rel="nofollow ugc">Deutsche Beschreibung des Plugins</a>
You run a Multisite Blogsystem with open registration for users to add own blogs and their can using a theme by 
different installed themes, but you want to show a link into the footers of the themes but only once time and for 
every blog another one?
With this plugin you can manage your outgoing links into the themes by a shortcode/function for every blog. You can 
set for every link the target, relation (Attribute rel), linktext and -title and the target url. Also you can set more 
than one link for a blog.
For output you can use a shortcode or a function . This function get the links 
for the current blog-id and printed this, if links are available.
All options/links can set by network admin only. The outputs needs no capability.

WPMU LinkManager

Manage your Themes footer links for every blog into a multisite includes with conditional tags.

Philipp15b

This plugin allows you to add your code/text to the headers and footers on all the blogs in the blog network and in the backend of all blogs too.
In addition, it is possible to replace the footer bar text in the backend completely.
You can access the settings under Network Admin -> Settings.

Sitewide (Admin) Header/Footer

Change the header/footer of the front- and backend of WordPress Multisite

WPMU LinkManager vs Sitewide (Admin) Header/Footer