What's the best approach to change an Absence plan from Hours to Days

Customer has several Absence plans for different countries, all based on hours and most of them have start on January 1th and some on different day.

Due to changed policy they would like to change from # hours per year to days per year. Because we cannot change the Plan UOM seems we have to create new plans.

Anyone had similar situation before? Can you share the approach and how to handle the carryover of previous year (hours) to new plan?

Thanks for your help

Wouter