Changing a pillow on rising can end in suffering (8)
I believe the answer is:
adapting
'changing' is the definition.
(adapting is a kind of changing)
'a pillow on rising can end in suffering' is the wordplay.
'pillow' becomes 'pad' (pad can mean a soft pillow or cushion).
'on' means one lot of letters go next to another.
'rising' says the letters should be written backwards (going up in a down clue).
'can' becomes 'tin' (synonyms).
'end in' indicates one should take the final letters.
The last letter of 'suffering' is 'g'.
'a' after 'pad' is 'pada'.
'pada' back-to-front is 'adap'.
'adap'+'tin'+'g'='ADAPTING'
(Other definitions for adapting that I've seen before include "Changing to suit a new purpose" , "Adjusting to suit a new use" , "Changing to fit new circumstances" , "Altering to fit another purpose" .)