Ty Wangsness of eMarketSouth posted a work-around you can use while the editing capability is missing from EE 2.
Unfortunately in the latest version of EE 2.0 (2.0.1 Build 20100121 as of this writing) the SAEF core files are incapable of supporting edit functionality… this post will show you how to correct that shortcoming (and hopefully the core hack required here will be implemented in some future version of EE).
Ty notes in the comments that this work-around is still needed for the newly release EE 2.1. I’m not sure that using the SAEF as an edit form has ever been officially supported by EllisLab but it is definitely a useful feature.
The fix, I want to note, requires a hack to the core EE code. Anytime you alter the core code you run the risk of your site breaking during any future upgrades. So, if you do implement this just keep a note of it.
Follow the instructions in Ty’s post and you should be set: How to Create Standalone Edit Forms in ExpressionEngine 2.0