Foot pedal that could be altered (7)
I believe the answer is:
treadle
'foot pedal' is the definition.
(I've seen this in another clue)
'could be altered' is the wordplay.
'could be' indicates anagramming the letters.
'altered' anagrammed gives 'TREADLE'.
'that' is the link.
(Other definitions for treadle that I've seen before include "requires footwork" , "Alerted (anag)" , "Rocker in a factory" , "Machine foot-lever" , "Foot lever giving power" .)