I read the following announcement on a mining pool website:
HardFork V3: 23 days from now
What will happen (if anything) to my actual wallet during this hardfork update? Will it change address? Do I need to do something to preserve/transfer my balance?
I created the wallet with simplewallet command-line client, version Monero 'Hydrogen Helix' (v0.9.4.0-release)
This answer is assuming you are on any 0.9.x version (lower versions would already have been booted off in the previous hardfork) currently. Note that 0.10 is going to be released soon. In general it is advised to use the latest binaries, because they contain bugfixes and new features.
What will happen (if anything) to my actual wallet during this hardfork update?
Nothing basically. The only (minor) change is that it will enforce coinbase transactions to be split in denominations. See line 123 of the dev logs.
Will it change address?
No. Addresses will never change during a fork.
Do I need to do something to preserve/transfer my balance?
No coins have to be moved. Thus, to answer you question, no you don't have to do anything.
You do not need to do anything to your wallet to prepare for the fork. The v3 fork will change not much at all to the network (just enforcing denomination breaking up for coinbase transactions). You will however need to update at some point to prepare for the next fork, v4, however. This is not ready yet, but will soon be.
In any case, short of a catastrophic problem, your wallet address will not change with a fork, and outputs will stay spendable after a fork. For example, RingCT transactions will be able to spend pre-rct outputs.
