Change same text across multiple PSD files?

You can open the files from within the script and there are multiple ways to specify the files:

1) If it is always the same files, you could hard code the paths to each into the script (this is the easiest, but not very flexible)

2) You could have the script call app.openDialog() which will bring up a file selection window where the user can select all of the relevant files

How you go about finding and replacing the text will differ based on how you have structured the .psd files (for example, is the text in its own layer?). Also if you make the structure and naming conventions (for layer names, etc...) the same across the documents it will make scripting the solution much easier.

If you posted an example or two of your files, I can help.

I created the minimal example below:

and wrote the following script which (I think) accomplishes your goal:

#target photoshop

var files = app.openDialog("Please select the relevant files");
var newTwitter = prompt("Type the new Twitter handle:");
var newInstagram = prompt("Type the new Instagram handle:");

for(var i = 0; i < files.length; i++) {
	var file = new File(files[i]);
	var docRef = app.open(file);
	var twitterLayer = docRef.artLayers.getByName("twitterHandle");
	twitterLayer.textItem.contents = newTwitter;     
	var instagramLayer = docRef.artLayers.getByName("instagramHandle");
	instagramLayer.textItem.contents = newInstagram;
	docRef.close(SaveOptions.SAVECHANGES)
}

Let me know if this makes sense of if you have additional questions!