pressed-signal of your button to a function looking like this:
$Label.text = "NewText"
$RichTextLabel.text = "NewText"
$RichTextLabel.bbcode_text = "NewText"
$Button.text = "NewText"
$Sprite.texture = load("res://icon.png")
$TextureRect.texture = load("res://icon.png")
The node-paths might look different depending on the location of (a) your Button and (b) the Label/RichtTextLabel/Button or Sprite/TextureRect you want to change. In the example I made the (rather unrealistic) assumption that all nodes a click on the Button changes are direct children of the Button-node and their default names are kept.