One way would be to place both textures on the object, with the one you want visible at the start and finish on top. You can order your textures in the Textures & FX panel of the Object Properties palette.
Now you can animate its visibility with the Stencil Channel control to let the other show through at the mid section of the animation. For more information see Texture Channel Controls in Chapter 9 of the User Guide.
You can also animate any of the attributes of a texture, using the Edit At controls at the top right of the Texture dialog. For more information see Animating Textures in Chapter 8 of the User Guide.