I recently changed the message in a Magic 8 Ball. The process was quite labor intensive, but anybody could do it.
1. Dissect 8 Ball (I recommend cutting around the seam of the ball and around the cup about 1/2 way up the side--save the blue solution in a bottle) 2. Remove the Icosahedrons and snap it apart (Exacto knives work well).
This is where it gets tricky... The goal is to create a message in raised letters where the tops of the letters all lie on the same plane--very important. 3. Cut apart the existing responses (words/letters) to construct your own message. 4. Using a rigid clear surface (A CD case works nicely), place a piece of 2-sided tape on the clear plastic surface. 5. Assemble your message face down on the 2-sided tape (placement is aided by using an Exacto knife). View message from opposite side to ensure proper alignment of words/letters. 6. Once a satisfactory message has been created, place the plastic/tape/message assembly on a table with the back sides of the words/letters facing up. 7. Cut an entire triangle from the Icosahedron (one that you didn't remove any words/letters from). The message should fit within the confines of the triangle (I suppose a larger backer could be used). 8. Using super glue gel, apply a drop of glue to the back of each word/letter. 9. Lightly place the triangle backer into the glue. 10. Allow glue to dry. 11. Remove from tape. You now have a suitable template from which to create your custom message.
I recommend creating a right pyramid--only four sides--for re-insertion into the 8 ball. To do this you must create four sides. 12. Obtain some 2-part epoxy and silly putty. 13. flatten the silly putty creating a smooth area larger than the message template. 14. Firmly press the template into the putty. 15. Placing a knife or screwdriver under one edge of the template, quickly flip the template out of the putty. This action, in conjunction with the properties of the putty will result in a perfect indentation. 16. Pour 2-part epoxy into the mold. (I recommend pouring the epoxy to the side of the indentation and allowing the epoxy to flow into the mold rather than pouring directly on the mold. This reduces trapped air.) 17. When epoxy dries, remove casting. 18. Cast additional sides as needed. 19. Using a toothpick and model paint, paint the letters of the message white (this requires a great amount of patience)
20. Pour a small amount of blue 8 ball solution in the bottom of the 8-ball cup. 21. Hold the cup over your head so you can see the new message--if the letters don't appear evenly or clearly you can even them out using additional layers of paint or by simply re-casting and hoping for better luck (my casting yields were only about 40%). Also, 'sweetening' the 8 ball solution helps--simply substitute 1/3 of the 8-ball water for tap water (this saves some aggravation).
22. One you have obtained four usable messages (I used 4 of the same), use a Dremel with the standard cutting disk. Cut the messages into triangular shapes and bevel the edges to produce a tighter fit. 23. Once a good fit is obtained, piece the triangles together using super glue gel to form a right triangular pyramid. 24. Check the pyramid for leaks and seal them as necessary (Epoxy is heavier than water--the pyramid must be hollow to float and function properly).
25. Place the pyramid in the cup and epoxy the cup back together. 26. Refill the cup with 'sweetened' 8 ball solution. 27. Epoxy the cup in place within the 8 ball--it will no longer fit tightly. 28. Neatly epoxy the two hemispheres of the 8 ball together. Smooth the epoxy with a piece of cardboard cut to fit the radius of the original groove in the 8 ball.
That's all it takes.
P.S. One final note: After I had the ball put back together I realized that only one of the four sides of the new polygon actually showed up because the polygon was not perfectly weighted. In retrospect, I should have made one message side and three blank sides. By weighting the polygon correctly, only the message side would be seen.