How to modify variables in other files?

Questions
1 
// conf.typ
#let font_size = 14pt
// or?
// #let DEFAULT = (font_size: 12pt, first_line_indent: 2em)

#let conf(doc) = {
  set text(font_size)
  doc
}

#let big(body) = {
  set text(font_size * 2)
  body
}

I want to modify the font_size and other variables in the main.typ.

// main.typ
#import "conf.typ": *
#show: conf

#lorem(20)

#big(lorem(20))

I want to find a simple solution.
Please!!