To change the target just hover a panel you want to edit and click that 'Edit' button at the bottom-right and enter a path of the folder or file you want to open when clicked, then save, refresh.
To change thumbnail right-click on a panel you want to edit, choose first option from the drop-down menu (now window appears) and replace/edit the 'bg.png' file, then refresh the skin.
Try adding quotes to the path. If it doesn't work, you'll need to wait till I update the suite, if you don't want to wait you can edit skin's ini file to see where's the problem...
=/ It's not work I hope you update the Suite in next time because I did not know what the problem is ^^... and in the ini-file I can not found anything I understand.
To change thumbnail right-click on a panel you want to edit, choose first option from the drop-down menu (now window appears) and replace/edit the 'bg.png' file, then refresh the skin.
Path=M:\TERA\TERA-Launcher.exe
But when I click on the Panel but nothing happens.