Workflow 7.1 SP2 ships with a Help Editor, which is where you can modify the component category. It's located at <install>/Designer/bin/WorkflowHelpEditor.exe.
When you open the Help Editor, choose File - Open select the .libconfig of the library in which the component resides (you can typically find this out by looking at the Settings tab of the component and looking at the namespace, it usually matches up)
Once the .libconfig is open, you can browse to your component, change the category, and hit Save. Reload Designer to see your changes.