About icon or text button it's not so easy ;)

Better to make a short cut...
Put this in the ShortCut board
for N by example! :)
script: if ( moi.majorVersionNumber == 3 ) { moi.ui.createDialog( 'nodeeditor/index.html', 'resizeable,defaultWidth:680,defaultHeight:420', moi.ui.mainWindow ); } else if ( moi.majorVersionNumber >= 4 ) { moi.ui.createDialog( 'moi://appdata/nodeeditor/index.html', 'resizeable,defaultWidth:680,defaultHeight:420', moi.ui.mainWindow ); }