I'm not aware of any setting for that. Single-clicking on a feature will show it's dimensions in the graphics area, where you can edit them directly (by single- or double-clicking, depending on whether or not you have Instant 3d turned on). Is that what you had in mind?
This is not possible through the FeatureManager Design Tree in SOLIDWORKS. There you need to select Edit Feature or Edit Sketch.
The other option is Instant3D (available on the Feature toolbar). When a sketch is set to Show, then you can double click this sketch to get into edit mode. But this is not available for features, because in this case you only show the dimensions of the feature.
A rectification on my earlier post:
Doubleclick on a sketch in the FeatureManager Design Tree works.
Thanks for all the great answers, this clarifies my question.
When I double-click on a feature in the graphics area, the dimensions of that feature are shown, and I can edit them, provided the part is shown shaded.
If the part is shown wireframe and I double-click the same feature, I don't see its dimensions. If I change the view of the part to shaded, there are the dimensions, waiting to be edited. The only way I seem to be able to use the double-click, edit functionality is to ensure the part is shaded.
Is this a bug, or is there a reason for it to happen (not to happen)?