The track is only closed Friday evening (late) until early Monday (very early) for the one weekend 2nd-5th May. Is it possible to reschedule your trip to the studios, to either the Friday or Monday. This will be a bank holiday weekend so the studio may well be at it's busiest.

http://www.networkrailmediacentre.co...ford-1e18.aspx

The London Overground service to Watford junction will still be operational according to Network Rail. This is likely to be the easiest option. There is a direct service from Euston. From elsewhere in London change at Willesden Junction. journey time from Willesden to Watford Junction is 15-20 mins less ( about 35 mins)
http://www.tfl.gov.uk/assets/downloa...etwork-map.pdf.

From Kensington your nearest options are likely to be Kensington Olympia or West Brompton from where it's a couple of stops to Willesden. Although depending on where exactly you are staying it may be easier to get the tube to Shepards Bush and then walk 1 min to the overground station (well signposted) and virtually next door)

There are about 3 trains an hour to Watford Junction on the Overground Service

Some possible alternatives
1- train to Radlett from Kings Cross then taxi
2 - dedicated coach service to the studio from London (see studio website) £29 transfer only return or £57 inc ticket
3 - tube to Watford then 20 mins walk to Watford junction
4 - taxi from Central London (expensive)
5- tube to Stanmore, where there is a taxi service that could take you there or to Watford Junction

Personally, if it's not possible to reschedule your visit I would go via the the overground service.