Some mishaps — alter your instrument (8)
I believe the answer is:
psaltery
'instrument' is the definition.
(type of musical instrument)
'some mishaps alter your' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'PSALTERY' can be found hidden inside 'mishaps alter your'.
(Other definitions for psaltery that I've seen before include "Ancient zither-like instrument" , "Obsolete stringed instrument" , "Dulcimer-like instrument" , "Plucked instrument; play rest (anag.)" , "plucky thing" .)