We never got this generation of Swift in Canada, so I had never heard of this variation. This is the only useful media coverage that found about it:I'm an owner of a Suzuki Hybrid which has an 1.2litre K12C engine. From what I know of the vehicle on the electric side of things with this car are for start/stop and some assitance when accelerating or when needing extra torque going up a hill. I know it has a small reworked Dualjet version of K12B engine and can also combined with 12-volt SHVS mild hybrid technology and 3Ah Lithium Ion Battery or a parallel hybrid system with 10 kW Motor Generator Unit (MGU).
(source : https://en.wikipedia.org/wiki/Suzuki_K_engine#K12C )
My question here is what is achievable with minor modification to the electric generator side of things? ideally to make my Swift better on petrol on the cheap I'd like to have an EV mode for around town. the petrol engine is fairly good on range as it is but having something that can extend the range further and fill in some power gaps like an electric supercharger would make for a fun ride!
2017 Suzuki Swift Hybrid unveiled
If I understand that article and the Wikipedia entry for this car correctly, the mild hybrid has the K14D turbocharged engine and your K12C-equipped car is a "full" parallel hybrid.
With minor modification of the motor-generator nothing of significance can be achieved. The PB05A motor is rated for 10 kW of output power and 30 Nm of torque (compared to 67 kW and 118 Nm from the engine); to get any more would require at least some modification of the controller/inverter which drives it.
If you can squeeze in a larger battery, you can get more electric-only range, but that won't help fuel economy very much if at all.