When you load a repository workspace normally it loads the current configuration which consists of all the change sets in the history of that repository workspace. So if you had a workspace where "Change Set 123" was the last one to be accepted or created (i.e is at the top of the history), then you would be loading what I belive you wanted. For example, in the Eclipse client, right-click on the component which contains "Change Set 123" and select "Show" --> "History". You would have to either discard or suspend all change sets which came after "Change Set 123" to get at a configuration which is based on the "Change Set 123". You can easily create (and load) workspaces based off baselines or snapshots however, so hopefully you have a baseline or snapshot of the point you want to load (or if it was captured in an RTC build, you should have snapshot which you can load as well), otherwise you are stuck discarding change sets which came after the one you care about (however a snapshot is ideal as it can capture the state of other components as well at a given point in time, whereas discarding from a component cannot).

(Side note: 'fancy' loading such as using "Load As", or load rules, will let you load a subset of files/folders as well as specifying where to load them, but will not help in loading a workspace at an earlier point in time.)