Editing an exisitng To Do does not allow to attach to existing feature
|Release time frame|
Currently, new to-do's can be created on features, ideas and many additional records throughout Aha! As you know, standalone to-do's can also be created.
At this time,because of the easy workaround of creating a new to-do, along with community feedback, we are unlikely to make updates in this area for this feature request. We hope you can understand.