Even if ungenerous, it's over a penny (3)
I believe the answer is:
tip
'even' is the definition.
The answer and definition can be both related to change as well as being verbs in their base form.
Perhaps you can see a link between them that I don't see?
'ungenerous it's over a penny' is the wordplay.
'ungenerous' becomes 'i' (I can't justify this - if you can you should give a lot more credence to this answer).
'it' becomes ''t' (abbreviation. e.g. in 'tis).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'a penny' becomes 'p' (short for pence).
'i' put after 't' is 'ti'.
'ti'+'p'='TIP'
'if' acts as a link.
Can you help me to learn more?
(Other definitions for tip that I've seen before include "Point of gratuity" , "Helpful information; end" , "Hint, suggestion" , "Piece of useful advice" , "Hint about a horse" .)
