Commercial liable to change (5)
I believe the answer is:
adapt
'change' is the definition.
(adapting is a kind of changing)
'commercial liable' is the wordplay.
'commercial' becomes 'ad' (abbreviation for advertisement).
'liable' becomes 'apt' (synonyms).
'ad'+'apt'='ADAPT'
'to' acts as a link.
(Other definitions for adapt that I've seen before include "Modify; acclimatise" , "Adjust (to new condition)" , "Convert to another use or situation" , "Modify, adjust" , "Adjust to new use" .)