Describing distinctive cultural group of 100 — cite changes allowing 50 in (6)
I believe the answer is:
celtic
'describing distinctive cultural group' is the definition.
(as in Celtic languages or culture)
'100 cite changes allowing 50 in' is the wordplay.
'l00' becomes 'c' (Roman numeral).
'changes' indicates anagramming the letters.
'allowing 50' becomes 'l' (I am not sure about this - if you are sure you should believe this answer much more).
'in' indicates putting letters inside.
'cite' anagrammed gives 'etic'.
'etic' going around 'l' is 'eltic'.
'c'+'eltic'='CELTIC'
'of' acts as a link.
(Other definitions for celtic that I've seen before include "Relating to Irish, Gaelic, Manx, Welsh, etc" , "Glasgow football club" , "Scottish club" , "Racial of Welsh, Irish etc." , "The Irish are part of the race" .)