To be honest, what you were contemplating is not that complicated. In fact, you can just set up a static function once in a new GDScript and load it as a resource, whenever you need to reuse it.
# new GDScript
# don't extend anything
static func premature_tween_stop(tween):
In another script:
var Utility = preload("res://Utility.gd")
var tween = Tween.new()
# start tween