When I deploy my files, the first statement at the top: "import { callbackify } from "util" " is added, but when viewing the website, I do not see my extension workin, and console shows an error being thrown at that statement. The Console shows "cannot use import statement outside of module"

hmmm i don't know about that, but you have another error, on the template.

template: "header_customizations_tpl",

should be the varialbe reference, not a string.

template: header_customizations_tpl,

Oh shoot, didn't catch that. I'll check that out. Thank you.