The most common and most likely answer to this crossword clue is the 8 letter word MODIFIED
I've seen this crossword clue in The Daily Telegraph
M
O
D
I
F
I
E
D
More clues leading to the result MODIFIED
- Changed doctor provided, that is, daughters come round
- Changed — assuming the writer’s in fashion with a bit of denim
- Supposing I put in condition daughter tweaked
- Changed doctor and stopped accepting life without protection
- Medic declined to cover condition that’s changed
- Softened, and second, faded around mid-life
- Government department, if that is dead, must be changed
- 1 Sacked right away after PM made changes
- Corrected overdose if I brought in medication
Buddy explains!

The straight part
We know that "tweaked" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tweaked = modified.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MODIFIED mean?
MODIFIED noun- Any vehicle used in modified racing.
- Changed; altered
- To change part of.
- To be or become modified.
- To set bounds to; to moderate.
- (grammar) To qualify the meaning of.