well...what I did...my inspection was due in jan so i took my car in late late december...they gave me a sticker for 2 years January...then jan. 1 i did my header install so i had 2 years to really worry about inspection...since the life expectency for most of my cars is 10 months on average I thought that was a pretty good plan
and what do you know I crashed it 9 months later
generally though most, id say, private inspections dont care as long as you pass the obd2 tests, thats not to say there arent some out there that are dicks about it...but the fines they could face im sure are astronomical so they have good reason really.