currying is not just for partial application

curry.scala

object Model {
  //the types don't mean anything, just faking some models.
  type Config = Float
  type ID = Int
  type Age = Int
  type DateInString = String
  type DateSinceEpoch = Float
}

//example of api changing where the first parameter is changed.
  import Model._
  
  case class AgeServiceClient(config: Config) {
    val getAgeOnDate_OldAPI: DateInString => ID => Age = ???
    val getAgeOnDate_NewAPI: DateSinceEpoch => ID => Age = ???
  }

  def modelMapping: DateInString => DateSinceEpoch = ???

  val getAgeOnDate: Config => DateInString => ID => Age
  = AgeServiceClient(_).getAgeOldAPI

  val getAgeOnDateRefactored: Config => DateInString => ID => Age
  = AgeServiceClient(_).getAgeNewAPI compose modelMapping
}

//example of api changing where the non-first parameter is changed.
object Demo2 {
  import Model._
  
  case class AgeServiceClient(config: Config) {
    val getAgeOldAPI: ID => DateInString => Age = ???
    val getAgeNewAPI: ID => DateSinceEpoch => Age = ???
  }

  def modelMapping: DateInString => DateSinceEpoch = ???

  val getAgeOnDateOld: Config => ID => DateInString => Age
  = AgeServiceClient(_).getAgeOldAPI

  val getAgeOnDateRefactored: Config => ID => DateInString => Age
  = {
    config => // in general, all the unchanged parameters up to changed parameter have to be explicitly passed in.
      AgeServiceClient(config).getAgeNewAPI(_) compose modelMapping
  }
}