Script for adding guides in the centerpoint of an object

i've written a public community utility for aligning objects via script which you can find here: https://github.com/wdjsdev/public_illustrator_scripts/blob/master/alignment_functions.js

(the alignment functions also have a dependency called "object_bounds_data.js" which can be found in the same public_illustrator_scripts repo). 

Using that, you can easily create a crosshair, and then align it to your selected object(s). Just save this code below into a new .js(x) file (or clone it from the github repo), select the item(s) in your document for which you want to draw guides, then execute this script and it will create a 10x10pt crosshair in the center of each selected item. 

You can preset the crosshair size by updating the "GUIDE_SIZE" constant. And you can determine whether to make true illustrator "guides" (the kind that are visible in the UI even if stuff is stacked on top of them, but won't print or display on any exported artwork), or you can choose to just make simple paths of a given stroke color. To toggle this setting, update the "MAKE_CROSSHAIRS_INTO_GUIDES" constant. true means they'll be guides. false means they'll be stroked paths.

Here's the link to the github page for this script: https://github.com/wdjsdev/public_illustrator_scripts/blob/master/crosshair_at_center.jsx

Let me know how it goes.

//author: William Dowling
//email: illustrator.dev.pro@gmail.com
//linkedin: https://www.linkedin.com/in/william-dowling-4537449a/
//github: https://github.com/wdjsdev
//Adobe Discussion Forum Post about this: https://community.adobe.com/t5/illustrator-discussions/script-for-adding-guides-in-the-centerpoint-of-an-object/td-p/13155180
//github link for this project: https://github.com/wdjsdev/public_illustrator_scripts/blob/master/crosshair_at_center.jsx

//*******//

//Did you find this useful? Would you like to buy me a cup (or a pot?) of coffee to say thanks?
//paypal.me/illustratordev
//<3

//*******//


//
//Draw crosshairs at center of selected items
//
//given at least one selected item, this function will draw crosshairs at the center of each item.


//arguments
//none. just select the items first and run the script.

//preferences
// MAKE_CROSSHAIRS_INTO_GUIDES:  boolean to determine whether the crosshairs should be 
//drawn as guides or as simple stroked paths.
    //if true, crosshairs will be converted to true illustrator guides.
    //if false, crosshairs will be drawn as simple stroked paths.

//GUIDE_SIZE: the height/width of the crosshairs in points.

//dependencies:
//alignment_functions.js: https://github.com/wdjsdev/public_illustrator_scripts/blob/master/alignment_functions.js
#include "alignment_functions.js"
    //the alignment functions also has a sub dependency called "object_bounds_data.js"
    //which is located here: https://github.com/wdjsdev/public_illustrator_scripts/blob/master/object_bounds_data.js
function makeCrosshairsAtCenter()
{
    //boolean to determine whether the crosshairs drawn should be
    //converted into true illustrator "guides" or not.
    //If false, crosshairs will be drawn as simple lines with a
    //stroke color of "crosshairColor" which can be customized below.
        //currently set to CMYK with 100% values for each. But you can choose
        //rgb, lab, etc. and set any values you want.
    const MAKE_CROSSHAIRS_INTO_GUIDES = true;

    const GUIDE_SIZE = 10; //number in points representing the width/height of the crosshair

    var doc = app.activeDocument;
    var layers = doc.layers;
    var sel = doc.selection;
    if(!sel.length)
    {
        alert("Please select at least one page item and try again.");
        return;
    }

    var crosshairColor = new CMYKColor();
    crosshairColor.cyan = 100;
    crosshairColor.magenta = 100;
    crosshairColor.yellow = 100;
    crosshairColor.black = 100;


    //since i don't know exactly what you want, i'm going to create a new layer
    //to plop all the crosshairs on. this helps avoid issues with trying to draw
    //or manipulate artwork on locked/hidden layers. If the items you're drawing
    //guides for are groupItems, you could simply put the crosshairs inside that groupItem.
    //entirely your call. Just update the "dest" argument in the "drawCrosshair" function call
    //to 

    //identify existing center guides layer, or create one
    var guidesLayer = (function()
    {
        for(var l=0;l<layers.length;l++)
        {
            if(layers[l].name === "Center Guides")
                return layers[l];
        }
    })() || layers.add();
    guidesLayer.name = "Center Guides";
    

    //loop through selected items and draw crosshairs on each item
    var curItem,curGuideGroup,curLine;
    for(var x=0;x<sel.length;x++)
    {
        curItem = sel[x];
        
        //create a crosshair group on the guides layer
        //change the second argument to "curItem" if you want the crosshairs to be drawn on the item itself
        //currently, curItem would need to be a groupItem.. But if need be, we can add logic to create
        //the necessary group structure and place curItem inside along with the guide. Let me know.
        drawCrosshair(curItem,guidesLayer);
    }


    function drawCrosshair(itemToGuideify,guideDest)
    {
        //make a group to hold the crosshair lines
        //this makes it easier to move stuff around later.
        //potentially this group could be named to match whatever
        //item it's marking. But it depends on whether the items you're
        //marking centerpoints for are named and whether it would even be
        //helpful to have the crosshair groups named. Up to you.
        //let me know if you want to change this and need some help.
        var crosshairGroup = guideDest.groupItems.add();


        //draw the horizontal line
        var crosshairLine1 = crosshairGroup.pathItems.add()
        crosshairLine1.setEntirePath([[0,0],[GUIDE_SIZE,0]]);
        crosshairLine1.filled = false;
        crosshairLine1.stroked = false; 
        
        //draw the vertical line
        var crosshairLine2 = crosshairGroup.pathItems.add()
        crosshairLine2.setEntirePath([[GUIDE_SIZE/2,GUIDE_SIZE/2],[GUIDE_SIZE/2,-GUIDE_SIZE/2]]);
        crosshairLine2.filled = false;
        crosshairLine2.stroked = false;

        //align the crosshairGroup to the center of the desired object
        //hint: you could use this very same logic to add "trim marks" to the corners of the object.
            //simply change last argument from "center" to "topLeft", then duplicate the crosshairGroup
            //and use the "align" function to align the duplicate to the top right corner of the object.
            //repeat for bottom right and bottom left.
        align(itemToGuideify,[crosshairGroup],"center");
        
        //check whether to convert to guides or not
        MAKE_CROSSHAIRS_INTO_GUIDES ? crosshairLine1.guides = true : crosshairLine1.strokeColor = crosshairColor;
        MAKE_CROSSHAIRS_INTO_GUIDES ? crosshairLine2.guides = true : crosshairLine2.strokeColor = crosshairColor;

        
    }
    
}
makeCrosshairsAtCenter();

Not a script, but an action.

Bounding Box Centre Guides

It's meant for single selected objects. Just select one and run the action.

This should be easily doable.  If you don't get an answer before then, I'll do it after work today.