Not to worry, I has a cunning plan...
My old lighting kit from the first TXT-1 I built, comes prewired with the correct resistor for 9v power; would I need to change it for ~6v use, or will it be alright as is pretty much ( just not quite as bright )?
I've seen a couple websites with great info/ interactive menus for picking the right resistor, but spending ~£2-3 on a couple resistors and postage seems daft since I tend not to create these kinda things very often.