Some clears it can but you are ok with the SPI if you use a good grade reducer and use the proper or next slower grade then the temp calls for.
For the second question, you must remember when you reduce solids, the clear will dry faster and cause it to flash faster, so it is important to know exactly what you want to do before adding reducer.
It is 75 degrees:
I want faster? Add 25% of 870 reducer.
I want just a little thinner but not change anything? Add 870 and keep under 5%.
I want flow or slower? Add 885 or 895 but keep under 5%.