Is it possible to write custom variables into FFSetVariables.txt?

[r.blake]

Still haven't figured out the answer to this question. The reply above seems to refer to something completely unrelated.

As an example - write a new variable into FFSetVariables.txt and then use said variable to define a gutter value during imposition

[burk11206]

Basic usage
Declaring a custom property is done using a custom property name that begins with a double hyphen (--), and a property value that can be any valid CSS value. Like any other property, this is written inside a ruleset, like so:

element {
--main-bg-color: brown;
}
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Note that the selector given to the ruleset defines the scope that the custom property can be used in. A common best practice is to define custom properties on the :root pseudo-class, so that it can be applied globally across your HTML document:

:root {
--main-bg-color: brown;
} Scentsy Login

[r.blake]

Is it possible to write custom variables directly into FFSetVariables.txt in a script, completely bypassing the need for having to generate and send csv files?