You can replace a texture colour swatch and all zones already painted with it will update.
 How to replace a texture swatch
How to replace a texture swatch
                                                            - In the Colour view, select the texture swatch that contains the bitmap texture you want to replace.
                                                                     
                                                                
- From the Colour View menu, select Colours > Edit Texture or double-click on the swatch.
The Browser window opens.
- Browse for the new PSD or TGA bitmap file created in a third party software.
                                                                     
                                                                
- Click Open to update the colour swatch.
                                                                    