The poll, which was conducted from July 7 to July 9, found that 73 percent of Democratic voters “somewhat” or “strongly” approve of Harris as Biden’s replacement. In an earlier iteration of the same survey, conducted from July 3 to July 6, a 66 percent majority of Democrats approved of Harris as a replacement.
I think the funds that the primary campaign got do actually go to Harris first. The DNC, PACs, and SPACs should be able to transfer like you said though.
Disclaimer: I’m not sure any of this shit is actually figured out. I doubt they thought about this situation when they wrote the FEC bill.