How often do search engine user-agents change, and do they change at all?

Question

Google

Hello!
I want to install Anti-Ddos from systemintegra, but I'm very afraid of search robots. Suddenly they block.
But they have a white list of user agents, and do they generally change with the search engines themselves or are they eternal (for example, from 2000 to this day they have not changed, I don’t follow this, so I’m asking here)? Suddenly they change and the bot will not be able to enter.
There is some fear in my heart. And I want to install Anti-DDOS so that http flooders finally fall behind ... They often flood because.

Answer 1

Large search engines generally try not to change the user agent.