how can I customize EDIT tab inside publisher portal?

I wanted to customize EDIT tab of publisher portal of wso2 registry. Currently we have below items:

Overview Categorization Contacts Interface Security Doc links Tags Taxonomy

I want to add one more item under Categorization such as below: "Classification" with drop down menu - vital, critical, discretionary

Please let me what to look for and where to look for in order to achieve this.

What you need to do is edit the relevant RXT and add a field element under the table categorization as follows

<field type="options" categorization="true">
  <name label="Classification">Classification</name>
  <values>
    <value>Vital</value>
    <value>Critical</value>
    <value>Discretionary</value>
  </values>
</field>

Please find the relevant documentation here to configure categorization options.