According to the documentation: https://docs.coronalabs.com/api/library/widget/newTabBar.html, there isn’t a method for doing this.
However, if you read the source, https://github.com/coronalabs/framework-widget/blob/master/widgetLibrary/widget_tabbar.lua, you can find out how the tab bar is made and how you can manually change the texts.
The code is copied from the documentation sample. I only added the last line.
local widget = require( "widget" ) -- Function to handle button events local function handleTabBarEvent( event ) print( event.target.id ) -- Reference to button's 'id' parameter end -- Configure the tab buttons to appear within the bar local tabButtons = { { label = "Tab1", id = "tab1", selected = true, onPress = handleTabBarEvent }, { label = "Tab2", id = "tab2", onPress = handleTabBarEvent }, { label = "Tab3", id = "tab3", onPress = handleTabBarEvent } } -- Create the widget local tabBar = widget.newTabBar( { top = display.contentHeight-120, width = display.contentWidth, buttons = tabButtons } ) tabBar.\_viewButtons[1].label.text = "I've been changed"