Yes, you can use a switched FCU as a means of isolation (i.e a switch ). What you do is use something like this as your switch.
And then run a cable in the wall from the switched side (i.e. the output) to a "flex outlet plate" which is one of these:
It may look like a blank plate, but there is a set of terminals inside, and there will be a hole for the flex to come out of (on the edge in this case, but you can get them where the flex comes out the front as well).
You should note, here I have assumed that you have the FCU at low level. If the FCU is high up the wall then you can run the cooker hood flex straight from the FCU. I wouldn't recommend having a low-level FCU with flex coming out, near a hob that could (would?) be a hazard.
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