Hi, I'd like to register my LHD in the UK and would need some advice on what changes are mandatory and who could perform the modifications and handle the paperwork for me.

Thanks

You'll need the EC Certificate of Conformity which shows the Type Approval Number among other things - and be able to show mph on the dashboard but that facility may be available already by changing electronic settings.

Headlamp patterns are complex, especially if you have HID/Xenons.