An <Articulation> element inside a channel definition in instruments.xml has no effect.
I am attempting to bring the documentation for the instruments file up to date (V3.5). I have found a number of problems that may be of no importance. Each is being reported as a separate ticket.
The old documentation states
"Articulation can be defined globally in museScore for all instruments, in each Channel for an Instrument and in an Instrument. They are overridden in this order."
At first sight the order of precedence seemed odd and on testing I found that an articulation in a channel had no effect whether the channel was named or whether you switch between channels with different articulation definitions.
I reduced the instruments.xml to show the effect (ChannelArticulation.xml).
1 Set instruments list 1 to ChannelArticulation.xml
2 Clear instruments list 2
3 Restart MuseScore
4 Start a new score with a clarinet part, fill some bars with quarter notes, select all and add staccatos
5 Play - no staccato
6 Add stave text with change channel - play - still no staccato.
I have assumed that the functionality no longer exists.