If you create and action, then change the source fixlet or baseline, the actin continues with the definition that existed when the action was taken - it will not inherit any subsequent changes to the source fixlet.
If you now create a new action, clients applicable to only the added fixlets will run the new action.
Clients applicable to both versions could run action 1, or action 2, or a mix of the member actions from both top-level actions. This selection or mix is indeterminate and will vary from client to client.
My preference in this instance is to stop the original action.