Premining documentation? I'm looking for more information on how to actually premine a coin. I would be grateful if someone can show me an example.

What I've tried so far does and not work, I'm basically mining the first block(not the genesis one) and it has a big reward but when I change the reward to a smaller one the blockchain is not valid anymore.

Thank you for any kind of tips documentation references.
Premining just means you can mine at your own at a very low difficulty before normal users have connected to your network. The size of the reward is determined by the protocoll so you cant change it until the procotol allows it (For Bitcoin it halfs ever 210000 Block). 

For example:

You can mine with a few hashs per second for a week. For bitcoin you get  a block every 10 minutes getting a reward of 50 BTC. This will give you 1008 Blocks and 50400 Coins. If you now  let other people connect they will start mining and the difficulty will increase.