By changing premix ratio from 40:1 to 32:1, you are indeed running a leaner air/fuel ratio, more oil less gas.
"will this account for more black crap coming forth from my silencer.." Yes, all other factors remaining equal (that's important).
When you say, 'more' that's saying you have some spooge already, so chances are nearly perfect that it's going to get worse.
I guess if your spooge is coming from burning tranny oil and NOT your premix oil it wouldn't matter.......;)
If leaning your A/F ratio is your intent, rejetting is the proper approach, not changing your premix.
Yes, slight changes to premix can be used as a tuning tool, but going from 40 to 32:1 isn't slight.
Spooge is generally considered to be not a good thing. My S/A exit is dry, my pipe-S/A joint is dry. I changed oil brands awhile back, and now get a bit of spit at the cylinder, but I don't worry 'bout it. I'd rather it wasn't there..but everything is working SO well, I don't care!
..pipe has been twanged more than once, unfortunately. A new one would likely fit better.
oh well....something else on my 'to-do' list.