using 32 amp or even 40 amp MCB's to protect a ring main is commonplace but only from the consumer unit to the first junction point-thereafter 26 amp ring main cable should be used but if something goes wrong with the intermediate cable in a single installation (from consumer unit to outlet)...
most older cooker outlets run (or should) run at least 30 amps so there shouldn't be a problem converting this to a standard double outlet.
but i would replace both the cable and the fuse/MCB at the consumer unit for safety's sake. the cable because you don't know how old it is or the...