If you already have a tag on a wiki page you can delete that tag by sending a request to the wiki page feed. Here's one easy way to do it with an asynchronous HTTP (Ajax) request using jQuery.
There is no a link to IBM Connections 4.x documentation.
Atom API Request Details
|Response||Status Code: 204 No Content|
Example using jQuery
Note: console.log can throw errors in IE, they are there for illustrative purposes only and should be changed as required.