You can find how you can disable the RadSplitter's embedded scripts here
. Please, note that we do not support client custom code which means that if you change the default scripts of a control and you experience problems with it later you should examine your custom code and resolve the issue on your own.
As far as I understood your scenario, you want to have some buttons on the top of the page but you the RadSlidingPanes to expand as they are in the left area of the screen. If so, you can achieve this without overriding the default scripts. What I can suggest in this case is to put the RadSlidingZone along with the RadSlidingPanes in the left area and hide the Tabs. After that you can expand and collapse the RadSlidingPanes by using their client-side API and perform the needed operation in client handlers of your buttons.
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