My hard top has the light tint, about 75% I believe. If I wanted to make them 35% can I just add 40% tinting?
Obviously 35+40=75, but I don't know if there are any tinting rules or weird things that happen when you want to tint already tinted windows.

I want to tint my fronts to 35% but only if I can make the rears darker than they already are to match.

 

I don't see why you couldn't, if you can find a shop that has the right %'s to match front to back. I believe the glass itself is tinted, therefore it won't matter if you add tint to it. Just take it to a shop and see if they can get you what you need. I'd think any good tint shop could.

 

The rear passener window is approx. 20%. The front is 75%. I had the tint man put 20% on the front and now the front window is 16%. The windows were tested with a tint meter at work before and after.

 

Your fronts ended up at 16% because of the factory tint added to the front windows. I am probably going to go with 25 so that the fronts are just a little bit lighter.