Associating an environment with a project would be a nice feature. It would be cool to be able to specify in the project settings which environment to use for this project, and this environment is automatically applied when opening the project. As far as I know this is currently not possible. Send a feature request email to IDM support.
By default there is the Select Environment
command in the MAIN
toolbar of all environments for quick selecting a different environment. Also possible would be to assign a hotkey to command EnvironmentSelectMenu
for faster opening the Environment Selector dialog.
BTW: Do you open the project from within UE or do you use a shortcut with the project file as parameter? If you use a shortcut, you can also use the command line parameter for the environment, see Open specific file in a different environment