i5/OS does not have support for the new rules in base R530 or R540. They do provide a PTF that automates this update which was release in the middle of November. IBM will support the new rules long before the Spring 2007 change date.
The change is made via PTF, and is part of Standard Maintenance. It only affects R530 and R540. The PTF numbers for base i5/OS are SI24906 for V5R3M0 and SI24908 for V5R4M0. These PTFs are immediate and do not require a system IPL
IBM has implemented a new keyword in RETAIN "DST2007". This new keyword has been implemented to help customers and IBM Service teams find relevant Daylight Savings Time (DST) information across all products.
If you prefer not to wait for the PTFs to activate this change, you can use WRKTIMZON option 2 for your zone to change the dates when the time zone change will occur. The recommendation is to install the PTFs in preparation for the Spring DST change.
There is an article explaining this change and how i5/OS supports it at MCPressOnline.com