How to change default 18 spaces tab indentation

In Scrivener the default tab indentation (the indentation pressing the tab key) is set to 18 spaces.
I would like to use scrivener to create a long technical document mixing text, images and lines of code.
Since using two or four spaces for indentation is a near-universal convention in many programming languages, I would like to know if it is possible to change the default 18 spaces, which makes my lines of code really difficult to read.