How do I genaddrecord and save it without any redirect on a click? I want this to happen in the back end.

first you'll need the image onload technique so you can load javascript pages on your forms/reports. After that's installed open up the page, add this code to edit or add views wherever you want it to run.

Then create a formula text button that you'll use to trigger it
Name the id of the button qbu_something instead of qbu_yourCustomBtn

dbidVariable should be the table ID like this
var dbidTableName = "aj867234jaf";

The example below create a record and assigns the related record value to the parent record id (kRid) you can type that in your console while on a record page and it will tell you the record id.
_fid_1 is your field ID that you're updated so in my case the related record field in the child table is _fid_10 and 9 is a text field and I enter purchase approved. 

then place this code after you've updated the values in that javascript page you made under the proper view (add/edit/report)

$('#qbu_yourCustomBtn').on('click',
            function() {
                $.post(dbidVariable, {
                    act: "API_AddRecord",
                    _fid_10: kRid,
                    _fid_9: "Purchase Approved"
                }, function(resp) {
                    console.dirxml(resp)
                   //Do something with the response.
                })
            });

Let me know if this makes sense or if you need direct help setting this up.
chuck@chuck.support
Good luck!