You'll have to use an EnergyPlus Measure to add this, as this object is not supported by OpenStudio.

I would:

1. Add a placeholder Chiller:Electric:EIR to create the appropriate nodes
2. Use an EnergyPlus Measure to swap out the Chiller:Electric:EIR for the Chiller:Electric:ReformulatedEIR
   • Make sure to remember to change the object type in the branch