Is it possible to add a custom field to the package variable?

try {
 const {
  purchaserInfo,
  productIdentifier
 } = await Purchases.purchasePackage(package);
 if (typeof purchaserInfo.entitlements.active.pro !== "undefined") {
  // Unlock that great "pro" content
 }
} catch (e) {
 /* No purchase */ 
}

Is it possible to add a custom field to the package variable?
I would like to access the field data through a webhook.