The resistor choice depends on ones systems character to begin with. Magnepan allows for attenuation of the tweeter for "brighter" or "hot" systems by allowing a resistor to be tried to tame tweeter.
My experience on this matter over numerous years of experimentation is that it was NOT the tweeter that needed attention. It was either ones front end or accessories added like power cords or other tonality changing tweaks.
Yes a resistor is an inexpensive way of so called tuning. My thought is look into what else is causing ones dislike of the tweeter. What we found setting up numerous Maggie systems were inferior power products like conditioners, PC, IC's and usually the culprit the speaker cable and jumpers.
With some systems though few the resistor was ALL the Doctor ordered. Not an easy task but fun along the path to Nirvana. Enjoys your journey and look in the right place.