The answer is pretty straightforward to anybody who is a programmer. Registry is just a configuration data that is read at some stage. The way the configuration affects OS or application (or DLL) depends on whether it has been read during the system-wide initialization (one off initialization that sets some flags only once after system restart), process/module-specific initialization (that is a one-off for a specific process or module), or is read anytime certain function is executed (thus, changing registry has an immediate effect).

It’s 2012 and time for something new, so I am suspending riddles for the time being. I still have a few more to post, yet from now on it won’t be that frequently.