Captcha while searching just for guests

[symptome]

I want to show a text for all guests that search in the forum and have to enter a captcha.
I want to tell them, that they don't have to enter the captcha when they're registered.

The Problem ist, that the phrase is also used in the part where someone registers and enters the captcha. And I don't want to tell somebody, that he should register, when he is already registering.
Can this phrase be splitt so that the search-function and the register-function use a different phrase?

Thanks!
Marcel