Starting or stopping Daylight Saving Time is not a timezone change. A timezone is — roughly — a set of timekeeping rules that some set of people use. DST is just part of those timekeeping rules. That is, your timezone is not the same thing as your UTC offset.
For example, the timezone America/New_York contains information not only about the UTC offset, but the offset during and not during DST, and when DST starts and ends. (And historical starts and ends to, so that UTC → local conversions (and vice versa) use the rules that were present at that time, not the rules that are present now, which may be different.)
E.g., my home desktop runs in the timezone America/Los_Angeles all year around. Most of my servers run in the timezone UTC all year. Both always have the appropriately correct time.
For example, the timezone America/New_York contains information not only about the UTC offset, but the offset during and not during DST, and when DST starts and ends. (And historical starts and ends to, so that UTC → local conversions (and vice versa) use the rules that were present at that time, not the rules that are present now, which may be different.)
E.g., my home desktop runs in the timezone America/Los_Angeles all year around. Most of my servers run in the timezone UTC all year. Both always have the appropriately correct time.