Took a dive over nothing to run through. 

(9 letters)

 

_ _ _ _ _ _ _ _ e

Took a dive over nothing to run through. 

(9 letters)

 

_ a _ _ _ _ _ _ e

jackknife … I think it must be.

🂻🔪

And you are spot on countess.

 

Took a dive over nothing to run through. 

(9 letters)

 

Took a dive - ?

over nothing - Jack

to run through - knife

Took a dive - Jackknife  (a dive in which the diver bends in midair to touch the toes, keeping the legs straight, and then straightens out).

 

Jackknife 

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

 

Trial……@@@?

No, not a trial.

 

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

 

_ _ _ i _

Stain.....

No, it’s stain-free.

 

Testing programme changes universal rating for nothing, harking back to a classic swell (5)

 

_ _ _ i _

 

There’s a charade, letter substitution, abbreviation, charade letter, reversal indicator…

 

Basic.....