how to reload old editor (again and again) with ajax calls?

hi guys
i have this problem

i have a textarea where i set with ajax the editor and my content.
in my editor i even added a personal button.

the problem is the following:
when i relize the event to reload with ajax the editor and the content i am able to get a new editor, but i cannot use the old configuration and the button i inserted is not visible anymore
can anybody help me?
in the meanwhile thank you !

this is the code loaded with ajax in a textarea

                   //CLEANING THE INSTANCE WHEN WITH AJAX I SET AGAIN MY DIV
                    if(CKEDITOR.instances["m_sTesto"] != undefined)
                        CKEDITOR.remove(CKEDITOR.instances['m_sTesto']);
                        
                    //FIRST TIME I LOAD THE PAGE => SO I SET MY NEW EDITOR WITH MY CONFIG
                    if( !editorCK)
                    {
                        var editorCK = CKEDITOR.replace(  'm_sTesto');
                                                    
                    }
                   //FROM THE SECOND TIME => I SET NEW EDITOR WITH MY OLD CONFIG AND I ADD MY OLD BUTTON
                    else
                    {
                        hInternalLinkButton = editorCK.ui._.items.internalLinkButton;
                        //CKEDITOR.replace( 'm_sTesto',  editorCK.config);
                        editorCK = CKEDITOR.replace( 'm_sTesto',  editorCK.config);
                        editorCK.ui.addButton( 'internalLinkButton', hInternalLinkButton);
                    }
                        
                     
                                                    
                    // Listen for the "pluginsLoaded" event, so we are sure that the
                    // "dialog" plugin has been loaded and we are able to do our
                    // customizations.                    
                    editorCK.on( 'pluginsLoaded', function( ev ){
                        // If our custom dialog has not been registered, do that now.
                        if ( !CKEDITOR.dialog.exists( 'internalLinkPanel' ) ) {
                            // We need to do the following trick to find out the dialog
                            // definition file URL path. In the real world, you would simply
                            // point to an absolute path directly, like "/mydir/mydialog.js".
                            //var href = document.location.href.split( '/' );
                            //href.pop();
                            //href.push( 'api_dialog', 'my_dialog.js' );
                            //href = href.join( '/' );

                            // Finally, register the dialog.
                            CKEDITOR.dialog.add( 'internalLinkPanel', '../internalLinkPanel.js' );
                        }

                        // Register the command used to open the dialog.
                        editorCK.addCommand( 'internalLinkPanelCmd', new CKEDITOR.dialogCommand( 'internalLinkPanel' ) );

                         // ADDING MY NEW BUTTON
                        editorCK.ui.addButton( 'internalLinkButton',
                        {
                            label: 'Collegamenti interni',
                            command: 'internalLinkPanelCmd',
                            //icon: 'http://gacela.labf.usb.ve/GacelaWiki/attach/Pic/playboy.png'
                            icon: '/manager/_editor/ckeditor_core/images/download.gif'
                        });
                    });