Disabling Modify can be achieved using custominit.html. The custominit.html is to be placed under the $MQ_COMMON_DIR/$MQ_COMMON_DIR/<enterprise_short_name>/htmlprops/ directory.

<SCRIPT type="text/javascript">
function customInit(){
    jQuery.each(jQuery("form[action=RecordUI]"), function(){   
    var rootFrame = jQuery("iframe[id=rootProductFrame]");
        if(rootFrame != null && rootFrame.size() > 0){
            var htaction = jQuery("#hiddenAction").val();
            if(htaction == "view"){
                window.__oldcheckForCanEditRecord = window.enableLink;
                window.checkForCanEditRecord = function()
                { var ret = window.__oldcheckForCanEditRecord(); var modifyBtn = jQuery("#actiontoolbarmodify_link"); if(modifyBtn) modifyBtn.addClass('toolbarButtonDisabled'); return ret; }
                    NewRecordUI.toolbar.oldManageAction = NewRecordUI.toolbar.manageAction;
                    NewRecordUI.toolbar.manageAction = function(obj, data)
                { NewRecordUI.toolbar.oldManageAction(obj, data); jQuery("#actiontoolbarmodify_link").addClass('toolbarButtonDisabled'); }
                ;
                window.__oldrelTableLoaded = window.relTableLoaded;
                window.relTableLoaded = function()
                { var modifyBtn = jQuery("#actiontoolbarmodify_link"); if(modifyBtn) modifyBtn.addClass('toolbarButtonDisabled'); window.__oldrelTableLoaded(); }
            }
        }
    });
}
</script>