1. Muting one or more instruments for playback and 2. Ritardando (slowing tempo)

Hi,

I have written an 8 parts/instruments for the song SHE'S LEAVING HOME composed by Paul McCartney from The Beatles. Flute, oboe, harp, 2 violins, viola, cello, 1 contrabass. I wish to know to know how could I mute the flute for instance when playing back the song on MuseScore?

My other question concerns tempo. I wish to know if there is a way to slow down tempo GRADUALLY with written indication above the staff. The key word being "GRADUALLY" because I already experienced LENTO and LARGO that slow down tempo drastically with success while what I want to execute is to perform this "GRADUALLY".
Look at the attachment. The song's original tempo is 127 bpm for the quarter note. I needed to slow down gradually the 3 last measures of the song, measure #147, #148 and #149. The only way I found that works fine is to assign a tempo change for the measure where you want to start slowing down the tempo: so at mesure #147, I slowed the tempo down from 127 to 120......then you assign a slower tempo for the second measure: so for measure #148, I slowed the tempo from 120 to 105.......and for the very last measure of the song ending with a fermata, measure #149, I slowed down the tempo from 105 to 60.
Any better way to realize that?

Thanks in advance for any tip,

Alain Gagnon