the dft "view" is definietly not law, not legal and not enforceable. My lawyer laughed her **** off when I first showed it to her.
the type-approval process applies only to new cars as designed by the manufacturer - we do not live in a state where any deviation from type-approved is prohibited. As an example, the Omega was type-approved with only a couple of makes of tyre, so if you fit Dunlops for example, then you break the law to just the same extent as DfT reference in this statement.
its difficult to see how this is going to be enforced at MOT, but even if it is, then you still won't be breaking the law using them.
all of the above comes with a proviso, that the installation you perform is SAFE. That's going to mean that you take appropriate steps to ensure that you don't dazzle other road-users.
the headlamp washers thing isn't really about safety per se, and the levelling system is there to ensure that a driver cannot forget to use the manual levelling system.
So, if you install a system such that the HiD bulb is in the same place as the H1 and you ensure that you never forget the manual leveling, then you're going to be safe and within the law.