Problem

I need the ability to add additional leaders to existing notes that have already been placed in my design file.

Solution (MicroStation v8i)

Solution #1 - Quickly add leaders (non-associative) to an existing note

It is possible to quickly add a non-associated leader to an existing note.
First, pick the Place Note tool (Tools>Text>Place Note).
With default tool settings selected, place a blank note (Text Editor left blank).
Snap the end of the new leader to an existing note's in-line leader as shown below. 
Although a new leader for the existing note has been visually created, it is not associated with the existing note or any surrounding elements.
Moving the note's text will clearly show how the new leader is not truly associated.

But, what if the additional leader needs to be associated to the existing note?

Solution #2 -  Add associated leader to an existing note

Ensure MicroStation's Association Lock is turned on.

To check this, navigate to Settings>Locks>Association and ensure the "Association" setting is toggled to ON.

Select the Place Note tool (Tools>Text>Place Note). Ensure the "Association" setting is checked within the tool settings window

Then place a blank note (Text Editor left blank) close to the existing note as shown:

Next, navigate to Tools>Manipulate>Modify>Modify Element.
Select (left-click) the tail end of the "new" leader and then move the leader to the intersection of the in-line leader and leader.
Left click to accept the modification. 

Test the newly created leader's associativity by clicking and dragging the note's text around the view window.
Both leaders (new and existing) should follow the text.
You can also use the Modify tool to associate a note's leaders to existing elements.

Solution (MicroStation CONNECT)

Solution #1 - Quickly add leaders (non-associative) to an existing note

Similarly to MicroStation v8i, it is possible to quickly add a non-associated leader to an existing note in MicroStation CONNECT Edition.
First, pick the Place Note tool (Drawing Workflow>Annotate Tab>Notes Ribbon Group>Place Note).
With default tool settings selected, place a blank note (Text Editor left blank). Snap the end of the new leader to an existing note's in-line leader as shown below. 
Although a new leader for the existing note has been visually created, it is not associated with the existing note or any surrounding elements.   

But, what if the additional leader needs to be associated to the existing note?

Solution #2 -  Add associated leader to an existing note

Ensure MicroStation's Association Lock is turned on.
To check this, navigate to the Drawing Aids tab within the Drawing workflow and select the Locks dialog launcher.
Ensure the "Association" setting is toggled to ON as shown:

Pick the Place Note tool (Drawing Workflow>Annotate Tab>Place Note).
Ensure the "Association" setting is checked within the tool settings window.

Then place a blank note (Text Editor left blank) close to the existing note as shown.



Next, select the Modify Element tool (Drawing Workflow>Home Tab>Modify Ribbon Group>Modify Element).
With default tool settings, select the tail end of the newly created leader and then move it to the intersection of the in-line leader and leader of the existing note by selecting (left-click) the point as shown:

Test the newly created leader's associativity by clicking and dragging the note text around the view window.
Both leaders (new and existing) should follow the text since they are now associated.

You can also use the Modify tool to associate a note's leaders to other existing elements.