fighter jets are complex things, you cannot simply bolt on something new and make a 3rd gen jet into a 4.5th gen jet.
1) integration issues. Mating brand new systems from a different country onto an old jet from a different country is very difficult, not impossible, but very hard.
2) Power issues. Modern systems like IRST, targeting pods, AESA need a lot of power, 3rd gen jets like Mirage III/5, Jaguar etc have limited power already
3) SU-30MKI, unless upgraded, is now technology that is over 30 years old, can no way be considered 4.5th gen