The matching rules are one part of a “workspace”. A workspace is a combination of project data, exclusion zone data and matching rules. The rules can only be set as part of publishing a workspace.
Having said that you can publish a new workspace (allowing you to apply new matching rules) by duplicating the existing data. You can choose to keep existing live data rather than uploading new files.
To do this, from the Data page. Select the existing live workspace “clone” option. As you step through the wizard, choose to keep existing data. Then you can change the rules and analyse/publish.
The process of publishing workspace is computationally intensive and results in a raft of notifications being sent out to users. This is why we don’t allow matching rules to be changed independently of a workspace.