Most of the registry tweak are HKEY_Current_USER. I'm wondering after i've finished the installation and I want to add new user account someday in future.

Will those HKECY_Current_user in unattended apply to the new account i create? I thought this only affect to one account when install windows.

Should I change to HKEY_LOCAL MACHINE if it can apply to new account?

All the current-user i have are un-hidedesktop icons, search url, start menu options, etc..

or should it be HKEY_USERS/.DEFAULT

Apply your registry tweaks at the T-13 stage of your unattended installation. All new users that logon will have those registry tweaks.

Check out MSFN's Importing HKEY_CURRENT_USER Registry Tweaks, which explains it all.