Changing $*DISTRO values for testing

I need to test a feature that includes this line:

if $translate-nl && $*DISTRO.is-win

I have tried to reassign a value to $*DISTRO,

$*DISTRO='Windows 10';

but it says:

Cannot modify an immutable Distro (debian (9.stretch))␤

$*DISTRO is a dynamic variable, and it makes sense that it's not modified. That said, is there any other way that code can be tested (other than going to Windows, of course)