I envision using 3 different logical actions (though maybe its only worth implementing one or two):
1. Convert this text into an inactive action in the same project/level.
2. Convert the current action into a project, and convert this text into an action in it.
3. The old action is done, but has spawned some related work: convert the selected text into a new action, maybe somehow connected to the old action, which is now marked as done, and is useful only as context.
As a preamble to my answer let me state the following: In my system I number each project with a serial number. This enables me to remember my most active projects by that number rather than try and search through a long list of projects to find the one I want. I also use sub projects quite frequently. These are numbered like, 010.1, 010.2 etc, for project number 010. In effect I try and have a structure in my project list, so as to enable me to easily access them, especially when I'm looking at them on the PC monitor.
What I would do for the case that you mention would be to create an inactive action in the project concerned instead of entering the task as a note. An inactive action would be naturally linked to the project (this probably tackles your third option), or you could convert it to a project (this maybe deals with your second option).