Modifications for Big Commerce Templates does not differ to the leading cms in these days. Big Commerce are using panels. BigCommerce provides user interface at admin to do the switching by dragging the panels from its place. Modifications in width , height,colors, font style, font colors , font-size in panels are very possible by editing it through the admin editor or through ftp. Big Commerce does not differ to wordpress cms which also provides at admin to edit the files for modifications.
Big Commerce also comes with their own API version of wordpress where we can call variables that are defined by their system.
The idea is, it’s not hard for the experienced developer to modify the properties of the BigCommerce if he has been into modification of the leading cms.