Setting FN settings across multiple files

Hi @SuzzyFlamingo it's actually pretty easy via a script, and I have just written one. See if it works for you.

- Mark

/**
 * @file Synchonize Footnote Options.js
 *
 * Synchronizes all open documents to match the active document.
 *
 * @author m1b
 * @version 2025-08-26
 * @discussion https://community.adobe.com/t5/indesign-discussions/setting-fn-settings-across-multiple-files/m-p/15474862
 */
function main() {

    var settings = {
        doc: app.activeDocument,
        activeDocumentID: app.activeDocument.fullName,
        docIDs: undefined,
        synchType: 'footnoteOptions',
        showUI: true,
    };

    settings.docIDs = getProperties(app.documents, 'fullName');

    if (settings.showUI) {

        var result = ui(settings);

        if (2 === result)
            // user cancelled
            return;

    }

    if (!app.activeDocument.hasOwnProperty(settings.synchType))
        throw new Error('Synchronize failed: bad `synchType` (' + settings.synchType + ')');

    var activeSynchOptions = app.activeDocument[settings.synchType].properties;

    for (var i = 0, doc; i < settings.docIDs.length; i++) {

        doc = getDocumentByPath(app.documents, settings.docIDs[i]);

        app.activeDocument = doc;

        doc[settings.synchType].properties = activeSynchOptions;

    }

    app.activeDocument = getDocumentByPath(app.documents, settings.activeDocumentID);

};
app.doScript(main, ScriptLanguage.JAVASCRIPT, undefined, UndoModes.ENTIRE_SCRIPT, 'Synchronize Options');

/**
 * Returns a document with matching path.
 * @author m1b
 * @version 2024-04-21
 * @param {Array<Document>|Documents} docs - the documents to look through.
 * @param {File|String} [path] - the path to search for.
 * @returns {Document?} - the Document, if found.
 */
function getDocumentByPath(docs, path) {

    path = String(path);

    for (var i = 0; i < docs.length; i++) {

        if (
            docs[i].saved
            && path === String(docs[i].fullName)
        )
            return docs[i];

    }

};

/**
 * Returns a property of each object.
 * @author m1b
 * @version 2023-09-08
 * @param {Array|Collection} things - the things to look through.
 * @param {String} key - the property name.
 * @param {*} value - the value to match.
 * @returns {Array<*>}
 */
function getProperties(things, key) {

    var found = [];

    for (var i = 0; i < things.length; i++) {

        try {
            if (things[i].hasOwnProperty(key))
                found.push(things[i][key]);
        } catch (_) { }

    }

    if (found.length > 0)
        return found;

};

/**
 * Shows UI for Synchronize Footnotes/Endnotes script.
 * @param {Object} settings - the settings to adjust.
 * @returns {1|2} - result code
 */
function ui(settings) {

    var w = new Window("dialog", 'Synchronize Footnotes/Endnotes', undefined, { closeButton: false }),

        // radio button
        sycnhTypeGroup = w.add('group {orientation:"row", alignment:["fill","center"], alignChildren:["left","center"], margins:[20,20,20,20] }'),
        marginGroup = sycnhTypeGroup.add('group {orientation:"row", alignment:["center","center"], margins:[0,0,0,5]}'),
        sortPreferenceLabel = marginGroup.add('statictext { text:"Synchronize All Open Documents:", alignment:["left","center"] }'),
        footnotesRadio = sycnhTypeGroup.add('radiobutton {text:"Footnotes"}'),
        endnotesRadio = sycnhTypeGroup.add('radiobutton {text:"Endnotes"}'),

        // buttons
        bottomUI = w.add("group {orientation:'row', alignment:['fill','top'], margins: [0,0,0,0] }"),
        buttons = bottomUI.add("group {orientation:'row', alignment:['right','top'], alignChildren:'right' }"),
        cancelButton = buttons.add('button', undefined, 'Cancel', { name: 'cancel' }),
        synchButton = buttons.add('button', undefined, 'Synchronize', { name: 'ok' });

    // initialize
    footnotesRadio.value = 'footnoteOptions' === settings.synchType;
    endnotesRadio.value = 'endnoteOptions' === settings.synchType;

    // event handling
    synchButton.onClick = function () {
        settings.synchType = footnotesRadio.value ? 'footnoteOptions' : 'endnoteOptions';
        w.close(1);
    };

    w.center();
    return w.show();

};