http://wheelstyleuk.alloysuk.com/ima...ary/offset.jpg
Think of it like this:
it would be +35, so to go to +40 the inner edge of the rim/tyre will be 5mm closer to the suspension strut, if they are the same width wheels
so the wheels wont fit the gaurds as well, and you will have less clearance between tyre and strut, which may cause rubbing
but if there is heaps of clearance between them it should go on fine.
just turn the fronts full lock and see if you can see the top of the tyre and put your fingers between that and the shock, check the rears too...
You drive an 06 Honda Civic yes? Offset is about +50 on all 4 wheels?
Don't expect any dish. Won't happen unless you go custom and like +70.