If I used APC and began the song with an intro with sync, when the intro was finished, is there any way to turn off the APC smoothly, so no cutoff noise is heard?

if the intro is 4 measures long, just increase it to 8 measures long.

the second 4 measures will be silent, and you can switch off apc and rhythm once the intro has ended. The cutoff will be clean and automatic.

i guess my real problem is ... is that I dont know how to extend an intro longer than it was made for...and they are usually 4 measrues. Your idea sounds right! Any thoughts on editing the intro...

just copy the style into the composer, select the relevant intro, and just increase the measure switch up to a max of 16 and OK it.

because you have done no copying and pasting the extra measures will be empty, silent, and the existing pattern will end cleanly.