Law they manipulated, becoming rich (7)
I believe the answer is:
wealthy
'rich' is the definition.
('wealthy' can be similar in meaning to 'rich')
'law they manipulated' is the wordplay.
'manipulated' is an anagram indicator.
'law'+'they'='lawthey'
'lawthey' is an anagram of 'WEALTHY'.
'becoming' acts as a link.
(Other definitions for wealthy that I've seen before include "Rich and prosperous" , "Affluent" .)