Strengthened in a polished way? (5)
I believe the answer is:
waxed
'polished way?' is the definition.
The definition and answer can be both related to change as well as being past participle verbs.
Maybe you can see an association between them that I don't see?
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for waxed that I've seen before include "Increased in phase" , "Became fuller" , "Grew larger" .)