opportunity hide/show elements via javascript

[eli.cohen]

Is the a way to disable/enable the issue export button via javascript on the announcement banner? 

for now I only found a way to completely disable it using css on the announced banner e.g to hide the single issue export button like described on they website.
div.aui-toolbar2-secondary {display:none}

I did some research but always got the same results only to hide it completely.
https://confluence.atlassian.com/jirakb/how-to-hide-elements-in-jira-using-css-or-javascript-958774526.html

Is it possible with plain javascript to also add a button on the system admin page which toggles the visibility of e.g the export button