Need to add parameters to thousand of drawings, parts & asm

You can use ModelCheck or DBatch - but those are a bit painful to setup and debug (in my opinion).

IF you want a quick solution - use CREOSON 

Here is a code example (slightly modified) from the PlayGround in CREOSON that creates/sets the same parameter across all prt files in session using a wildcard (e.g. *.prt) . -- you can do the same for assemblies and drawings just change the wildcard extension.

let paramObj = new creo.ParameterObj();

 paramObj.file = '*.prt'; // <<-- ENTER CREO FILE and EXTENSION (can be wildcard)

 paramObj.name = 'NEW_PARAM' // Parameter 'name' 
 paramObj.value = 'HELLO!' // Parameter 'value'
 
 paramObj.set();

If you want to do the same for ALL Parts in a Working Directory by loading each model into memory one at a time.... you can do something like this (modified from the sample code in the CREOSON PlayGround):

function setParam(itemName) {
 let paramObj = new creo.ParameterObj();
 paramObj.file = itemName;
 paramObj.name = 'NEW_PARAM';
 paramObj.value = "WOW!";
 return paramObj.set();
}

function processItem(itemName) {

 let fileObj = new creo.FileObj();
 fileObj.display = true;
 fileObj.activate = true;
 fileObj.file = itemName;

 return fileObj.open()
 .then((itemName) => {
 return setParam(itemName)
 });

}

function batchFiles () {

 let creoObj = new creo.CreoObj();
 let creosonUtilObj = new creo.CreosonUtils();

 creoObj.filename = "*.prt"; // <<-- ENTER CREO FILE (*) and EXTENSION
 
 creoObj.list_files()
 .then(function (respObj) {
 return creosonUtilObj.loopItems(respObj.filelist, processItem)
 })
 .then(function () {
 alert("Finished Batching!");
 })
 .catch((err) => {
 alert('ERROR: '+err);
 });

}

// START THE BATCH PROCESS!
batchFiles();

Note the above code leave everything in session within Creo - so you would have to add a save operation after each update to be more complete.

Hope that helps!

Dave