Nothing wrong with that except you will have to change the time back one hour when the original DST date kicks in unless you uncheck the 'Adjust the clock for daylight savings time' box in the clock . Same two adjustment needs will happen in the fall also if you leave the DST box checked.
Tzedit is a way to make a permanent change that fixes both the start month and day of week, and the end month and day of week, for DST for all future years.
Thanks for the most useful lesson. Much appreciated.
I have XPPro S2 is TZ edit good for that? I read there were some conflicts around with differnt Windows vesions.