Relink PNG to PSD

Thank you for all the input. the relink in the links pallet is the one that looks like the best fit for us. I will try some of the scripts also. Leaving them RGB doesn't really work for our work flow.

Here's a script I use for my workflow. It resaves the selected image as psd-file in photoshop as relinks it on InDesign.
However, it doesn't convert to CMYK, but a line of code can be added for this.

— Kas

Try this below snippet : 

// You can include whatever Extension you wish for it in this below list for relinking
var extension = ["psd", "png"];
//============================================
var myDoc = app.documents[0];
for(var i = 0; i < myDoc.links.length; i++){
    var imageName = myDoc.links[i].name.split(".")[0];
    var folderPath = File(myDoc.links[i].filePath.replace(/\\/g,'/')).parent.fsName.replace(/\\/g,'/');
    if(myDoc.links[i].status.toString() != "NORMAL"){
        for(var x = 0; x < extension.length; x++){
            if(File(folderPath+"/"+imageName+"."+extension[x]).exists){
                myDoc.links[i].relink(File(folderPath+"/"+imageName+"."+extension[x]));
                break;
                }
            }
        }
    }
//============================================

Best

Sunil

There’s also no need to make the conversion to CMYK in Photoshop, the same conversion can be made from InDesign on an export to PDF or from the print RIP. On an Export, simply set the Output tab’s destination to Document CMYK and the RGB PNGs will be converted into your document’s assigned CMYK space.