How to manually assign acquisition program?

We host all content in a content program, for example landing page for white paper XXX, and use the same landing page for different channels. There are separate programs for each channel. We want to assign the channel program name as acquisition program, but it always automatically assigns the content program as the acquisition program. I thought about two solutions, but both have big cons.

1. put a wait step before the content program flow actions, this will delay the auto responder email to the lead. (this may not even work, because the acquisition program could be assigned when moment a lead is created before all flow actions )

2. add "change acquisition program value when it's empty", this will also change other existing leads' acquisition program.

Anyone knows how to catch the acquisition program information correctly in this scenario?

Thanks!