main.tf

variable "version" {}

locals {
  versions = {
    v2 = {
      "app.mydomain.com" = "abcd.region.elb.amazonaws.com" 
    }
    v1 = {
      "app.mydomain.com" = "xpto.region.elb.amazonaws.com"
    }
  }
}

resource "aws_route53_route" "routes" {
  for_each = local.versions[version]
  # ...
}