In E17 You can change everything (Letters , LettersColors , Colors , Borders , Modules etc.....) , except what does not exist.
If I do not think the edges of both sides, logically you can not change that configuration, simply does not exist.
But , from the themes manager, "advanced tab" , if you can put whatever you want from a theme to another

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Example , a theme without borders to the sides, choose a theme based on theme that has borders to the sides, easy.
Is E17

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Greetings:
Agust