Replace Object During Animation I am looking to replace an object with another object during an animation. I want the original object to be in the animation up until I 'replace' it. I do not want to replace the original object throughout the entire animation.

What I am doing is essentially sliding letters onto a cylinder, and they are being spun around the cylinder. (Like at a playground, cylinder goes through the middle of the letter and you can spin it). By the way, each letter has been converted to a mesh (so I could animate them)

Example:
--WOW--
--YES--  

I want wow to be visible (staying still), and then animate the letters to be spinning. During the spin animation I would like to replace the first W with Y, O with E, 2nd W with S. Still spinning. Letters stop spinning to say YES.

I have found multiple explanations for how to replace an object throughout the entire animation, but not on how to do the above. I'm not sure what the best way is to go about it, is there a way to "replace" the letter so it stays in the same spot, and continues the animation (almost) seamlessly - using a keyframe to set when the letter gets replaced, or make the 1st set of letters somehow go instantly invisible, with the new set becoming visible during the same frame?
One way to do this is by using the Mask modifier :


select the two meshes and click  Ctrl+j to join them
in edit mode assign each word to vertex group 
add Mask modifier and add the vertex group
in animation Right click on the icon next to the vertex group in the modifier and select add Keyframe 
clicking  the icon will switch the visible words






result :