Steps to customize dashboard (Transactions as an example)
1. Navigate to Transactions > Transactions Overview > Settings portlet > Click Edit Custom Tab
2. Content tab > Portlets sub tab > Add additional portlets like 'Custom Search'
3. If you want multiples of any portlet types this can be done by adding the portlet type multiple times
4. Adjust audience settings if required and save
Be aware that the tabs are based on center type and audience settings may need to be adjusted.