manual/include/independent-and-dependent-midi-region-copies.html

<p>
  When <dfn>copying a MIDI region</dfn>, Ardour has to decide whether to make the
  copy refer to the same data as the original or not. If it does refer
  to the same data, then editing either the copy or the original will
  affect the both of them. If it refers to an independent copy of the
  data then each one can be edited without affecting the other.
</p>

<h2>Changing dependent/independent copying for the entire session</h2>

<p>
  <kbd class="menu">Sesson &gt; Properties &gt; Misc &gt; MIDI region copies are
  independent</kbd> can be used to control the default behaviour when
  making a copy of a MIDI region. 
</p>
<p>
  When enabled, every new copy of a MIDI
  region results in a copy being made of the MIDI data used by the
  region, and the new copy of the region will refer to that data. 
</p>
<p>
  When disabled, every new copy of a MIDI region will refer to the same
  MIDI data, and thus editing any copy will change the contents of all
  of them.
</p>
<p>
  Changing the status of this option has no effect on the existing
  dependent/independent status of existing region copies.
</p>

<h2>Making an existing copy of a MIDI region independent</h2>
<p>
  Context-click on the MIDI region you want to be
  independent. From the context menu, select <kbd class="menu">MIDI &gt; Unlink From
  Other Copies</kbd>. The copy is now using an independent version of
  the data, and edits to the copy will affect only the copy. Other
  copies will continue to share data.
</p>

<p class="note">
  Note that the copied data only covers the extent of the region when
  the copy is made. If the region was already trimmed and then a copy
  is made, an independent copy will have no access to data that is
  earlier or later than the bounds of the region it was copied
  from. Put differently, if you make an independent copy of a trimmed
  MIDI region, you cannot "untrim" it to a larger size.
</p>