To elaborate on that "no."
It depends.
If I change winlogon registry values, I restart the netlogon service and the
changes are immediate.
If I change SNA (a mainframe communication protocol) values, I restart the
SNABASE service and changes are immediate.
And, as Wesley wrote, other changes can be put into effect by restarting the
explorer.exe process. This was especially effective with Windows 9x when
changing local policies.
Moral is: If the registry entries have an associated service or process,
restart it, and you probably will have immediate realization of your regedit
modifications.
Good luck
Joe