Assign member group to user without registration/login

Hello,

is it possible to assign a member group to a user that is not logged in and has not registered an account (aka. guest)?
I know that you can define a default member group that is automatically assigned to guests, but is it also possible to manually
set and change this member group via for example a custom module?

To be more specific, I want to implement an option in the frontend that allows the users to assign themselves to one of two member groups
without having to register an account.

Quote:

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Originally Posted by SamK

Hello,

is it possible to assign a member group to a user that is not logged in and has not registered an account (aka. guest)?
I know that you can define a default member group that is automatically assigned to guests, but is it also possible to manually
set and change this member group via for example a custom module?

To be more specific, I want to implement an option in the frontend that allows the users to assign themselves to one of two member groups
without having to register an account.

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Are you talking about users and members? I think that member is what you're talkin' about. Right?

This is not right, that you can define a default member group that is assigned to guests.

No, an incognito visitor can not assign to anything. How should Contao recognize this visitor when he comes back to the page later?

A guest in the FE is not a user nor a member. So he can not assign to a member group without registration. A guest can register himself and chose one ore more groups out of multiple but then he is registered. And when he logs in he can be recognized by Contao.