Cartridge Impedance


I just bought a phono pre-amp that allows me to adjust the impedance of a MC cartridge. I was using 100ohms. Now I want to experiment.
Could someone tell me the effect the trebles will have if I lower or raise the suggested impedance. For example, If I raise the impedance will the highs be more prominent or less prominent? 
Thank you.
128x128jmh128
Poor English is something up with which I shall not put! Ha! 
Your pedantry is beyond my annoyance. But I thought your post was cute.
Let's see, I split the infinitive "to annoy".  But most people don't know what an infinitive is, these days.  And the rule on that has loosened by convention. What else?

Seriously, my message is that if you learn something more than merely the answer to your simple question, perhaps next time you won't have to ask.  Also, I personally cannot stand knowing the answer (to almost any factual question) without at least trying to discover the why of it.