I had a few Suzuki Swifts called "Metro" in the states, a few 1.0L and two were 1.6L 16V. Those were more like motorcyles on four wheels, the exact opposite of the 1.0L, although there was little difference in fuel consumption. See TeamSwift forum.
As an owner of the 1.0L Mirage, I would not think conversion from 1.2 to 1.0 makes much sense.
Related thread:
Thread: Poll: 1.0L Mirage engine = 7.5% better fuel economy. Would you choose it?
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View my fuel log 2014 Mirage ES 1.2 manual: 62.4 mpg (US) ... 26.5 km/L ... 3.8 L/100 km ... 74.9 mpg (Imp)