Bad idea.
Not sure I understand the motivation to lower impedance as a whole. It's not the impedance that defines performance but, often, the performance decides the impedance. I'm gonna get flamed for oversimplifying.
That being said, if a resistor was placed parallel to the speaker and crossover, as a whole, it should not affect the crossover. If you were to reduce or raise impedance of any individual driver after the crossover, that would dramatically change the way the crossover functions.
Then, you have to consider wattage rating on the resistor.
Not sure I understand the motivation to lower impedance as a whole. It's not the impedance that defines performance but, often, the performance decides the impedance. I'm gonna get flamed for oversimplifying.
That being said, if a resistor was placed parallel to the speaker and crossover, as a whole, it should not affect the crossover. If you were to reduce or raise impedance of any individual driver after the crossover, that would dramatically change the way the crossover functions.
Then, you have to consider wattage rating on the resistor.