Asset creation on cryptocurrency/blockchain I have a question regarding the creation of a blockchain application. 
In bitcoin its predetermined before the genesis block is even created, to only release a limit of 21 million bitcoins. Examples such as ripple and ethereum also release the amount of coins they have in their blockchain on creation.

Is the possibility to determine asset on a blockchain only available at the creation? 

Lets say for example I want my blockchain to have 1000000 monkeycoins as assets, but 4 years later I want to add another 500000 monkeycoins and maybe 5 years after that another 500000. 

Is it a must to say I want 2 million coins in assets on creation or can I add a random amount as long as everyone in the network agrees on the creation of the asset?
That depends on the protocol you are using to create the assets.

For instance, with Colu's Colored Coins protocol (a protocol that works on top of Bitcoin), the issuer of an asset explicitly specifies if the asset is reissuable in the future or not (when he first issues the asset). If the asset is issued as locked, then even the issuer can not reissue more units of the same asset in the future. On the contrary, if the asset is issued as unlocked, then the issuer is able to reissue more units in the future. Note that if the asset is unlocked, then the issuer alone may decide to create new units of the asset (there is no need for the "network" to agree on this).