The result of all ecommerce IT development is the delivery of a commerce platform. This platform should be viewed as a product that has its own life cycle, will undergo improvements and will eventually be decommissioned. Typical for any software product is that it is fluid and needs an can be adjusted continuously until it is replaced by a new platform.
The most common way to start a new platform or the development or a replacement of an existing platform is to start a project, which will deliver the platform as the end result. This will be the start of the improvement phase of the project.
A project has three axes: scope, budget and time. most of the time, two of the three are fixed, leaving room on the third axis. So, if budget and time are important, there is room in the scope.