Here are many extended techniques on the clarinet to help you increase the repertoie of sounds available as a composer or player.
Different ways of fingering notes. Notated by verbal instruction and fingering diagram. There is no need to specify fingerings normally, so the use of alternative fingerings is generally left to the player. There should be a very good reason for specifying alternative fingerings!
Quartertones and Microtones
Intervals smaller than a semitone. Notation: notations vary, but the examples shown seem typical of quartertones and raised & lowered inflections. Microtones on the clarinet are practicable, but obviously need a great deal of care and attention to detail. Consultation with the player is probably the best way forwards. Microtones on the bass clarinet are much more problematic, because of the covered holes.
Playing chords - more than one note at a time. The notation is to write the bottom note of the chord and the word 'chord' above. Occasionally composers write all the notes of the chord that they wish to hear and/or provide a fingering diagram. Although specialist manuals often give highly detailed fingerings for chord production, the variability of instruments, players and playing techniques makes it difficult to assume a specific effect from a particular fingering.
Singing and playing into the instrument simultaneously. Write the sung notes in small noteheads, plus verbal instruction. It is possible for voice and instrument to sing and play either the same or different notes, and for both to move independently of one another (Watch out for the vocal range!). For extended passages it may be easier read if the sung line is on a separate stave to the played line.
Blowing air into the instrument without producing a tone. May be pitched (write verbal instruction above the note) or unpitched. Pitched air notes are very quiet. Unpitched notes may be made louder by allowing air to escape around the mouthpiece. 'Half and half' (i.e. half an embouchure) is quite effective in the low register of the bass clarinet.
Removing the mouthpiece and blowing into barrel. Another verbal instruction (may be pitched). Perfectly possible, but not particularly effective. More effective is to buzz the lips and produce tones as if it were a trumpet - in this way it is possible to play tunes over a range of about an octave.
Violent release of the tongue, creating a 'slap' as the vacuum is opened. Notation is a verbal instruction. It is mainly a bass clarinet effect.
Clicking instrument keys notated by x-shaped noteheads and verbal instruction. Relatively quiet on clarinet, but quite effective in the low register of the bass.