Persisted in one's efforts, though terribly tired (5)
I believe the answer is:
tried
'persisted in one's efforts' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe there's a link between them I don't understand?
'terribly tired' is the wordplay.
'terribly' is an anagram indicator.
'tired' anagrammed gives 'TRIED'.
'though' is the link.
Can you help me to learn more?
(Other definitions for tried that I've seen before include "checked out" , "Made an effort" , "heard in court" , "Proven by experience" , "Essayed" .)