Full Idea
A disposition is subject to 'altering' when the stimulus of the disposition influences whether (and to what degree) an object has that disposition. Either a live wire goes dead when it is touched, or a dead wire has a sensor making it live when touched.
Gist of Idea
A disposition is 'altered' when the stimulus reverses the disposition
Source
Friend/Kimpton-Nye (Dispositions and Powers [2023], 2.2.2)
Book Reference
Friend/Kimpton-Nye: 'Dispositions and Powers' [CUP 2023], p.11
A Reaction
The word 'fink' is used of such interference. Not much of a problem, I would say, because at the moment when the stimulus comes to do its job, there is no longer a disposition for it to trigger. No different from switching off a light.