Add my own symbols in my score

i'm a young contemporary composer and a great part of my work is about pure sound, sound modulation as we can ear in Acousmatic music.
To achieve such results we need a notation for extended technics, and this notation doesn't exist in musescore
i'm looking forr arrows we can stretch, plain creshendos for pressure augmentation (that we can stretch too)
and i'm not talking about importing PNGs (not stretchable, we just can adjust the scale)
i'm currently switching between musescore and photoshop to add my symbols but it's not efficent (at all)

is there any way too add our own symbols that we can use as the creshendo, foot pedal
maybe in the file sytem of musescore

sorry for my english, it's far to be my first language

Thank you

(an exemple of what i'm looking for)
https://www.youtube.com/watch?v=8j0LcmdG1kI