Board Thread:Support Requests - Getting Technical/@comment-3537355-20140607191224/@comment-366087-20140607203737

To change what the current labels say, you go to MediaWiki:User-identity-box-group-sysop, where "sysop" is for Admin. Similar pages include -bureaucrat, -founder, chatmoderator, -blocked, etc. (do not change -staff). Changing what is at these pages will change the label for ALL in each group. This is easy and basic.

The link Tupka provided is good for individualizing custom tags, although somewhat advanced.