This might not be that straight forward, generaly the message is there because of ui_no_results message token. You can customize this in iiqMessages file. Hovewer as you see it’s not certification specific so it migh most probably change text in a lot of places.
Here second option is possible - you can write fairly simple plugin to change it, this plugin will allow you also to make remaining changes as I believe OotB it’s not possible to do that via configuration.
sure - if you use SSD you can just put the file into web/WEB-INF/classes/sailpoint/web/messages/iiqCustom_XX.properties where XX is your lanquage, en for english, de for german and so on. Format of the file is fairly simple - it’s token - value for example widget_direct_reports=Mein Team.