Hello.
I have no doubt, you can replace the shrouded plug and the test leads are reaching their origin specs.
The point is: The specs for the Cat- Ratings have changed.
To be "up-to-date" needs new leads.
Differences to the "old" Cat- Ratings:
1. For the Cat IV Rating it is necessary, that the tip of the probe is insulated (except the first 2 mm).
For the Cat III Rating there is no need for that, the well known 16 mm tip is enough.
2. The lead must indicate, if the insulation is damaged, e.g. the lead has an inner hull of white silicone,
the outer hull is red. You can immediately see, if the red insulation is damaged.
3. The contact in the shrouded plug must have an insulation at his top. To avoid under every circumstances
to have contact with a part under current/voltage.
(Who figures that out? Is there really anyone, who sticks the probe into the mains and poke with his finger,
just for fun, into the plug of the test lead?? A volunteer candidate and uprising hero of the Darwin-Award?)
Question: Why don't you make it simple and sell the multimeter without probes? (It is not unusual.)
Greetings,
Hartmut