Mark again registered gratitude ultimately to house painter (7)
I believe the answer is:
regrade
'mark again' is the definition.
('grade' can be a synonym for 'mark' so perhaps 'regrade' is OK for 'mark again')
'registered gratitude ultimately to house painter' is the wordplay.
'registered' becomes 'R' (abbreviation, as in registered trademark).
'ultimately' says to take the final letters.
'to house painter' becomes 'grade' (I can't justify this - if you can you should believe this answer much more).
The last letter of 'gratitude' is 'e'.
'r'+'e'+'grade'='REGRADE'
Can you help me to learn more?
(Other definitions for regrade that I've seen before include "Rank again" , "Alter rating" , "Give new status" .)