To customize the Adaptive Form( appearance, layout etc), please go through the "Customize" section of the documentation : https://helpx.adobe.com/aem-forms/6-1/help-tutorials.html
If that doesn't help, could you tell what you want to achieve by overriding HTML code for the guideContainer ?
I want to change the main form layout to fit my requirements.
Maybe there is a best way to change the layout of the form? what if my requirements are with a layout that is not fully compatible with the AEM defaults?
i have read many times the documents with out luck with this... the "tutorials" in the adobe documents are very basic and in those tutorials they tell you "do this, paste this code into that .jsp..." but they don't tell you WHY that code goes there.. or WHY you copy that node...