I think that Mehran 2016 also comes with factory CNG option.... if you want a cng car then go for the FF cng one.
For your question:
Yes CNG can be installed in Mehran and it works but there are a lot of disadvantages listed below:
1- Your car's warranty will be void
2- The petrol fuel avergae of your car will be reduced
3- You are going to face reliability issues as it is very common with CNG installation in efi cars
4- The air filter needs to be frequently changed in CNG cars, remember that the airfilter of MEhran E2 is damn expensive.
I have owned two Mehran Euro II since 2013, one is still with me 41K on ODO.............. car is very good on petrol (14-15 kmpl with AC in city - 16-18 kmpl without AC in city)