Through what procedure is canon law amended? The Code of Canon Law has undergone at least one other version since the first in 1917, and has received amendments since the 1983 version from what I've read. 

What would warrant a new version of the Canon Law? How exactly are smaller amendments applied to the Code of Canon Law?
A pope is supreme legislator (albeit subject to the Supreme Legislator) in the Church; he, as Vatican I declared, &quot;has primacy of jurisdiction over the universal Church of God&quot;.
The word &quot;jurisdiction&quot; etymologically has the sense of &quot;[the right] to declare law&quot; (ius law + dictio &lt; dicere declare).
A pope promulgates Canon Law binding on the whole Church.

Can. 7 A law is established when it is promulgated.
Can. 8 §1. Universal ecclesiastical laws are promulgated by publication in the official commentary, Acta Apostolicae Sedis, unless another manner of promulgation has been prescribed in particular cases. They take force only after three months have elapsed from the date of that issue of the Acta unless they bind immediately from the very nature of the matter, or the law itself has specifically and expressly established a shorter or longer suspensive period (vacatio).

cf. canonist Dom Augustine on 1917 can. 8 ff.