Converting RGB images in InDesign using Photoshop's 'Convert to Profile'

You could try this - I don't have files to test it on but added some extra functionality that should work

Again I'm not the best at this - ceratinly not working blind as nothing to test with 

function convert2CMYK() {
    var doc = app.activeDocument;
    var selection = doc.selection;

    if (!selection || selection.length === 0) {
        // No selection, process all images in the document
        var links = doc.links;
        for (var i = 0; i < links.length; i++) {
            var link = links[i];
            if (link.status === LinkStatus.NORMAL) {
                var image = link.parent;
                if (image.constructor.name === "Image" && image.space === "RGB") {
                    processImage(link);
                }
            }
        }
    } else {
        // Process selected items regardless of shape
        for (var j = 0; j < selection.length; j++) {
            var selectedItem = selection[j];
            if (selectedItem.constructor.name === "Image") {
                var selectedLink = selectedItem.itemLink;
                if (selectedLink && selectedLink.status === LinkStatus.NORMAL && selectedItem.space === "RGB") {
                    processImage(selectedLink);
                }
            } else if (selectedItem.images && selectedItem.images.length > 0) {
                for (var k = 0; k < selectedItem.images.length; k++) {
                    var nestedImage = selectedItem.images[k];
                    var nestedLink = nestedImage.itemLink;
                    if (nestedLink && nestedLink.status === LinkStatus.NORMAL && nestedImage.space === "RGB") {
                        processImage(nestedLink);
                    }
                }
            }
        }
    }

    UpdateAllOutdatedLinks();

    //===================== FUNCTIONS ===============================
    function processImage(link) {
        var newPath = DuplicateAndRenameFile(link.filePath);
        var profile = getCMYKProfile();
        if (profile) {
            CreateBridgeTalkMessage(newPath, profile);
            RelinkFile(link, newPath);
        } else {
            // alert("No CMYK profile selected. Conversion canceled.");
        }
    }

    function CreateBridgeTalkMessage(imagePath, profile) {
        var bt = new BridgeTalk();
        bt.target = "photoshop";
        bt.body =
            "(function() {" +
            "    var psDoc;" +
            "    app.displayDialogs = DialogModes.NO;" +
            "    psDoc = app.open(new File('" + imagePath + "'));" +
            "    if (psDoc) {" +
            "        psDoc.convertProfile('" + profile + "', Intent.RELATIVECOLORIMETRIC, true);" +
            "        psDoc.save();" +
            "        psDoc.close(SaveOptions.SAVECHANGES);" +
            "    }" +
            "    app.displayDialogs = DialogModes.ALL;" +
            "})();";

        bt.onError = function (errObj) {
            // alert("Error in BridgeTalk: " + errObj.body);
        };

        bt.onResult = function () {
            alert("Image successfully converted to CMYK!");
        };

        bt.send(30);
    }

    function UpdateAllOutdatedLinks() {
        var link, c;
        for (c = doc.links.length - 1; c >= 0; c--) {
            link = doc.links[c];
            if (link.status == LinkStatus.LINK_OUT_OF_DATE) link.update();
        }
    }

    function DuplicateAndRenameFile(filePath) {
        var file = new File(filePath);
        var folderPath = file.path;
        var fileName = file.name;
        var fileExtension = fileName.substring(fileName.lastIndexOf("."));
        var baseName = fileName.substring(0, fileName.lastIndexOf("."));
        var newFileName = baseName + "_C" + fileExtension;
        var newFilePath = folderPath + "/" + newFileName;

        var newFile = new File(newFilePath);
        if (file.copy(newFilePath)) {
            return newFilePath; // Return the path of the duplicated file
        } else {
            alert("Failed to duplicate and rename file: " + filePath);
            return filePath;
        }
    }

    function RelinkFile(link, newPath) {
        var newFile = new File(newPath);
        if (newFile.exists) {
            link.relink(newFile);
            link.update();
        } else {
            alert("Failed to relink file: " + newPath);
        }
    }

    function getCMYKProfile() {
        var profiles = [
            "Coated FOGRA39 (ISO 12647-2:2004)",
            "Coated FOGRA27 (ISO 12647-2:2004)",
            "Coated GRACoL 2006 (ISO 12647-2:2004)",
            "ISO Web Coated",
            "ISOnewspaper26v4",
            "Japan Color 2001 Coated",
            "Japan Color 2001 Uncoated",
            "Japan Color 2002 Newspaper",
            "Japan Color 2003 Web Coated",
            "Japan Web Coated (Ad)",
            "U.S. Sheetfed Coated v2",
            "U.S. Sheetfed Uncoated v2",
            "U.S. Web Coated (SWOP) v2",
            "U.S. Web Uncoated v2",
            "Uncoated FOGRA29 (ISO 12647-2:2004)",
            "US Newsprint (SNAP 2007)",
            "Web Coated FOGRA28 (ISO 12647-2:2004)"
        ];

        var profileName = showDropdown(profiles);
        return profileName;
    }

    function showDropdown(profiles) {
        var dialog = new Window("dialog", "Select CMYK Profile");
        dialog.orientation = "column";
        var dropdown = dialog.add("dropdownlist", undefined, profiles);
        dropdown.selection = 0;
        dialog.add("button", undefined, "OK", { name: "ok" });

        if (dialog.show() == 1) {
            return dropdown.selection.text;
        } else {
            return null;
        }
    }
}

convert2CMYK();

What I'm trying to do

Selection Handling:

• Full Document Processing: Processes all images in the document if no selection is made.
• Selected Items: Processes only selected images or nested images within selected objects.

Image Conversion:

• RGB Detection: Checks if the image is in RGB colour space before converting.
• Photoshop Integration: Uses BridgeTalk to send instructions to Photoshop for profile conversion.

File Management:

• File Duplication: Creates a duplicate file with _C appended to the filename before conversion, preserving the original.
• Relinking: Relinks the duplicated and converted CMYK file back to the InDesign document.

CMYK Profile Selection:

• Dropdown Interface: Allows users to select a CMYK profile dynamically using a dropdown menu.
• Profile List: Provides a comprehensive list of predefined CMYK profiles.

Link Management:

• Link Status Check: Ensures links are active and normal before processing.
• Outdated Link Update: Updates any outdated links in the document after processing.

Error Handling:

• Error Messages: Alerts users about issues such as failed duplication, relinking, or BridgeTalk errors.
• Fallbacks: Prevents further steps if prerequisites like CMYK profile selection fail.

Additional Features:

• BridgeTalk Customisation: Allows integration with Photoshop for automated conversion without user intervention.
• User Feedback: Displays alerts to confirm the successful conversion of images.