Is there a script to change a setting incrementally when batch processing in Camera Raw?

Copy and paste the script into ExtendScript Toolkit

This gets installed with Photoshop and can be found:-

PC: C:\Program Files\Adobe\Adobe Utilities

MAC: <hard drive>/Applications/Utilities/Adobe Utilities

Start Bridge

PC: Edit - Preferences - Startup Scripts

Mac: Adobe Bridge menu - Preferences - Startup Scripts

At the bottom click the "Reveal Button" this will open the folder where the script should be saved.

Close and restart Bridge.

Accept the new script.

To use:-

Navigate to the folder with your Raw files.

Tools - Set Average Exposures

Make sure you do a test first on a temp folder of the raw files!

#target bridge   
   if( BridgeTalk.appName == "bridge" ) {  
setExposure = MenuElement.create("command", "Set Average Exposures", "at the end of Tools","exp");
}
setExposure.onSelect = function () {
var d=app.document;
d.deselectAll();
var sels = d.getSelection("cr2,crw,nef,mos,orf");
var noOfFiles =sels.length;
var diff = (3.25 / (noOfFiles-1));
var exp = 1.25;
var exp2=exp;
for(var a = 0;a<noOfFiles;a++){
    exp2 = exp - (diff*(a)).toFixed(3);
    var file = new File(sels.spec.toString().replace(/\....$/,'.xmp'));
    setExposure( file, exp2 )
    }
app.document.chooseMenuItem('PurgeCache');
function setExposure( file, expose ){
     file.open('r');
     file.encoding = "UTF8";
     file.lineFeed = "unix"; 
     file.open("r", "TEXT", "????");
     var xmpStr = file.read();
     file.close();
     if (ExternalObject.AdobeXMPScript == undefined) ExternalObject.AdobeXMPScript = new ExternalObject("lib:AdobeXMPScript");
     var xmp = new XMPMeta( xmpStr );
     xmp.setProperty( XMPConst.NS_CAMERA_RAW, "Exposure", Number(expose) );
     file.open('w');
     file.encoding = "UTF8";
     file.lineFeed = "unix"; 
     file.write( xmp.serialize() );
     file.close();
    };
};