Yes, if you keep the headtube unchanged and put a smaller wheel on, you will steepen the headtube angle.
I suppose if you added on the difference between the height of the two wheels to the headtube, the HT angle would stay the same.
As far as trail goes, as i said you want it to be in the low 40s. A bike with 40mm trail and a bike with 100mm of trail will handle completely differently.
Yes, if you keep the headtube unchanged and put a smaller wheel on, you will steepen the headtube angle.
I suppose if you added on the difference between the height of the two wheels to the headtube, the HT angle would stay the same.
As far as trail goes, as i said you want it to be in the low 40s. A bike with 40mm trail and a bike with 100mm of trail will handle completely differently.