improvisatoryadjective
/ˌɪm.prə.vaɪˈzeɪ.tər.i//ɪmˌprɑː.vɪˈzeɪ.tɔːr-/(of speech or music) done or performed without having been planned exactly, making something up as it is being performed:
an improvisatory dance/song
The music allows for improvisatory variation.
his improvisatory collaboration with director André Gregory