Ok thanks already for your input Tim.
Yes, leads are coming through a form fill and depending on what the lead enters to particular questions (knock out criteria) I want to place them in stream 1, 2, or 3. Ad choice how you described it sounds like a possible solution, but with the ad choice function I cannot determine the KO criteria.
Until now I am using the "Add to engagement" and also define the stream in the drop down. Sometimes i am also usning add choice e.g. "Not filled out form" and define the stream where the lead should move into. Though leads are always ending up in stream 1 (default).
Of course it would be possible to create another stream where all leads move into and then simply use "Change engagement program stream", so that would be possible but I do not want to even enlarge the campaign.