Custom image import into Photos.app using PhotoKit. Import an original JPEG plus an edited version of it. Proof of concept.

CustomPhotoImport.swift

import Cocoa
import Photos

let original = URL(fileURLWithPath: "/Users/matt/Code/personal/PhotoKitPlayground/Test/DSC_6326.jpg")
let edited = URL(fileURLWithPath: "/Users/matt/Code/personal/PhotoKitPlayground/Test/DSC_6326-edit.jpg")

let status = PHPhotoLibrary.authorizationStatus(for: .readWrite)

if status != .authorized {
    PHPhotoLibrary.requestAuthorization(for: .readWrite) { status in
        if status == .denied {
            assertionFailure("Photo access is required")
        }
    }
}

func addAsset(image: URL, editedImage: URL, to album: PHAssetCollection) {
    PHPhotoLibrary.shared().performChanges {
        // Request creating an asset from the image
        guard let creationRequest = PHAssetChangeRequest.creationRequestForAssetFromImage(atFileURL: image) else { return }

        // Request editing the album
        guard let addAssetRequest = PHAssetCollectionChangeRequest(for: album) else { return }

        // Get a placeholder for the new asset
        guard let placeholder = creationRequest.placeholderForCreatedAsset else { return }

        // Set the edited photo as an adjustment
        let output = PHContentEditingOutput(placeholderForCreatedAsset: placeholder)
        let editedData = try! Data(contentsOf: editedImage)
        try! editedData.write(to: output.renderedContentURL, options: .atomic)
        output.adjustmentData = PHAdjustmentData(
            formatIdentifier: "customImport",
            formatVersion: "1",
            data: "📸".data(using: .utf8)!
        )
        output.renderedContentURL
        creationRequest.contentEditingOutput = output

        // Add the placeholder to the album editing request
        addAssetRequest.addAssets([placeholder as Any] as NSArray)
    } completionHandler: { success, error in
        if !success, let error = error {
            error
            print("error creating asset: \(error.localizedDescription)")
        }
    }
}

let collectionOptions = PHFetchOptions()
collectionOptions.predicate = NSPredicate.init(format: "title = %@", "Import")

let assetCollections = PHAssetCollection.fetchAssetCollections(with: .album, subtype: .any, options: collectionOptions)
let importAlbum = assetCollections.firstObject!
importAlbum.localizedTitle

addAsset(image: original, editedImage: edited, to: importAlbum)