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.

Silkalns

WP Chill

Remove or replace footer credits (or any text or HTML in page) before page is rendered. With this plugin there is no need to modify code such as footer.php which if done incorrectly can cause your site to break or new theme updates will stomp over your changes requiring you to remove footer credits on each update.
This plugin has very minimal options to keep things simple and easier to use. You enter the text or HTML that you would like to find in one text box and the text or HTML that you would like to replace in another text box (or nothing to remove). Go <a href="https://cpothemes.com/remove-powered-by-wordpress/" rel="nofollow ugc">here</a> to view my step by step tutorial with screenshots and video.

Remove Footer Credit

It seems to work, but not as intuitive as it should be. You need to copy the code that makes up the footer porting you wish to move and paste that into the box. Wish there as a way to simply way to remove it.

Seems to Do Nothing

Remove or change footer credits or any text or HTML without modifying code.

WPMU LinkManager vs Remove Footer Credit