Asset creation on cryptocurrency/blockchain
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).