Well, if want to compare to Japan and US.
In Japan, any licensed garage can do inspection your cars something like an MOT certified garage in the UK. Inspection is done every 2 years.
Here's the few main thing that they will check.
Exterior
Tailpipes: Tailpipes are not allowed to protrude past the car's body however tailpipes that are built into the side of the vehicle are allowed.
Body kits/Aero parts: Aerodynamic mirrors, windage trays under the tail section of the car and body kits using front bumper scoops are allowed. However all aerodynamic parts must fit and be molded correctly so they are flush with the car's body.
Fenders and Overfenders: All fenders and overfenders (including widebody style-kits) must not inhibit the turning of the car's wheels (which must be able to turn 30 degrees inward and 50 degrees outward).
Spoilers: All spoilers (aftermarket or OEM) must not be wider than the car's rear and must be bolted to the car's trunk.
Tail-lights: LED and traditional bulb tail-lights are allowed for all vehicles as well as European style fender turn-signals. However American style rear tail-lights and non amber-color turn-signals are not allowed.
Windows: No tint can be present on driver and passenger side windows however commercial UV window blocker is allowed. Lexan windows are not allowed unless they are approved via a case by case basis. Stickers/banners on the front windshield and rear glass are not allowed. Etching on the windows, with the exception of VIN information, is not allowed.
Speedometer
The speedometer of the car is tested by driving up on to a dynamometer. The vehicle will be accelerated to 40 km/h twice and the vehicle's speedometer reading will be recorded; should the reading be different, it will not pass.
Headlight
All headlights must be aligned to be in a straight line with their height on the car. Halogen, HID and bulb style head lights are allowed. All headlights must have the same color when turned on
(It means if you use 8k HID your parking light must be the same colour). Headlight swaps, making pop-up headlights into normal headlights, rally-car style multiple headlights and putting trim around headlights is allowed.
Exhaust/Muffler
Cars that are 10 years and newer must have carbon monoxide measurements of 1% and hydro-carbon output of 300ppm. Cars older than 10 years must have carbon monoxide measures of 4.5% and hydro-carbon output of 1200ppm. High flow catalytic converters are allowed however gutted ones are not. All O2 sensors must be in working order along with any oil catch tanks. Mufflers when tested for noise output will be tested at a 45 degree angle at a 50 cm distance. For vehicles 10 years and younger the max level allowed is 96 dB (decibels). For vehicles over 10 years of age the max level allowed is 103 dB.
Suspension
All bushings must not be broken or in bad condition. All control arms must be in working order. There can be no rust/corrosion on springs, struts or other suspension components. If the car has 4 wheel steering it must be working. The vehicle must also meet minimum height requirements which will be checked by referencing the lowest part of the vehicle (not including the suspension components). For vehicles with 200–249 cm wheelbase they must be 8 cm off the ground and vehicles with 250–299 cm wheelbase they must be 9 cm off the ground. For all other vehicles for every 50 cm over 299 cm in wheelbase add .5 cm to the minimum height and for vehicles under 200 cm in wheelbase subtract .5 cm to the minimum height.
Interior
General interior equipment must be still intact (ie: dash). Roll cages (must have padding around bars) and carpet removal are allowed. Bucket seats must measure 420 mm from left to right bank but can not be over 450 mm from left exterior side to right exterior side (total width of seat). Aftermarket seats made of fiber-reinforced plastic are not allowed. Any holes or rips in seats must either be taped up or repaired.
All in all can consider not that strict on mods since most of the aftermarket parts made by those japan companies are all tested to meet the R&R before selling to buyers.
While in the US, the regulations varies among the states as they govern their own vehicles regulations and not under 1 system so if your exhaust is legal in 1 state it might not be legal at another states. In most states inspection is done annually. DMV is their JPJ.
This is for California state
http://www.arb.ca.gov/msprog/aftermkt/replace.htm
What I can say is that our JPJ R&R are not as complete as the Japs and US... for us the R&R can always be different from mouth to mouth...the books says this can but the officer says the other thing....the japs and US made the R&R clear so that aftermarket parts manufacturer, shops all know what can be done to the car legally...and the authority there doesn't care about those small small things like emblem, logo..etc
Another thing is the people selling the parts....when you fix the part...they will say not problem one..legal one...but when go through road blocks than kantoi....Yes there are still illegally modified cars both in Japan and US same like here...