Unfinished clue I'm altering, about utopian's head in clouds (6)
I believe the answer is:
cumuli
'clouds' is the definition.
(cumulus is a kind of cloud)
'unfinished clue i'm altering about utopian's head' is the wordplay.
'unfinished' means to remove the last letter.
'altering' is an anagram indicator.
'about' indicates putting letters inside.
'head' says to take the initial letters.
The first letter of 'utopians' is 'u'.
'clue' with its final letter removed is 'clu'.
'clu'+'im'='cluim'
'cluim' is an anagram of 'cumli'.
'cumli' going around 'u' is 'CUMULI'.
'in' acts as a link.
(Other definitions for cumuli that I've seen before include "Clouds of round masses heaped on horizontal base" , "Globular clouds" , "Rounded clouds with flat bases" , "Plural of clouds heaped on horizontal bases" , "Fluffy clouds" .)