WordPress has a nasty habit of storing absolute URLs in the database. That means that all internal paths, including images and other resources are stored in the database containing the base URL of your blog alongside the URI of the resource. It is not possible to change WordPress URL quickly. Or at least I thought so.
There could be multiple reasons for disabling updates of plugin or a theme. For example, in time constraint, you have reached for desperate measures and edited the source of a third party plugin or theme. Now, that is the practice that is bad on so many levels, but sometimes you just have to deliver in time, no matter what.