Chemical Registration Configuration guide says the following on these two topics:

Preventing Direct Registration

To prevent direct registration by a specific user or group, ensure they are explicitly Denied the Chemical Registration > Register Entities permission.

Limiting Access to Read-Only

To prevent a user or group from having any registration ability (so that they can only view the home panel of the web client) you can:

1. Assign them to the Logon group and no others.

2. Ensure that none of their groups have either of the RegisterDirectly or RegisterEntities permissions.