Sauce Labs' service is intended to be set up as closely to a stock customer environment as possible. We make limited changes to browser & registry settings, Apple defaults and other configurable options. We don't generally install extra video codecs, browser plugins, .Net frameworks, or similar products.
There are several customisation options available to customers requiring changes to the standard environments. Please note that Sauce Labs support does not extend to customisation options, and having these in your tests may limit the support we can provide with other issues as well.
If you need to make changes to Browser settings, some browsers allow you to do this directly with Selenium, as described in this article from Selenium HQ. Our KB article Creating Custom Firefox Profiles and Chrome Instances also has some examples of ways to customize browser settings and functions.
For making changes to the environment, you may be able to use a prerun executable, as described Setting Up Pre-Run Executables.
If your changes are applicable to multiple customers and can't be achieved through prerun executables or Selenium profiles, consider raising a feature request.