http://www.mcmurrayhatchery.com/product/caponizing_kit.html
If you are going to do it , you should purchase a proper kit. The effects of this operation , if done succesfully are usually the following.
1. the bird becomes more docile.
2. The saddle feathers and tail feathers grow longer. (fishing fly enthusiasts love capon feathers)
3. The bird will usually become heavier, this is due to less activity, (capons are great eating), but both size and delectabililty are determined by breed. In my r
As far as the moratlity rate going up (once they survive the operation), I found the opposite to be true.
Quote "Mr. Maurizio Lanzoni from Villa Poma rears about 40,000 pure-bred Hiline capons on his industrial farm.
The chicks are given only vegetable feed and are caponized when they are 2545 days old, according to the poultry bred. The mortality rate is very low, about 2-3% and they can survive longer than chickens, say, till they are 200 days old."
Here is a university paper that explains the what why and how well.
http://www.oznet.k-state.edu/historicpublications/pubs/SB315.PDF