Annual Increment Policy As Per Calender Year

Greetings !!
Myself working in Korean MNC company, which is into auto component manufacturing with overall employee strenghth less than 100
In our Head quaters side in Korea they are considering calender year Jan to Dec for annual increment process
Here in India side I was using standard method April to March, but now My management has asked me to make policy as per jan to Dec
Can you support me in telling the cutt off date for eligiblity, and some guidelines for making policy
Thanks & Warm regards
AKG

You can take all confirmed employees and/or over 6 months as eligibility criteria as on 31st Dec.

increment, performance review, confirmation, etc is all internal policies of the company.
There is nothing to stop you from shifting the appraisal and increment dates to January.
you can keep everything else same, just shift the dates of review and implantation of the increment.