With Sass there are possibility to define variable as !default and can override it before import the script

_tokens.scss

tb-custom-primary: #014d5b !default; //Is the value if not defined in final scss
tb-primary: tb-custom-primary;
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index.scss
$tb-custom-color: #34b232; //Now I can define the final value for variable
@import '_tokens'
it would be useful to add it in ThemeBuilder UI.