You'll have to do that at the projects; there's no way to do that at BOINCstats/BAM. If you have duplicates on your combined stats from different projects, you can try temporarily attaching the host to all projects you've ever crunched for, that should update the CPID at all of them. Unfortunately, that doesn't always work if there are projects that are having difficulties--though if the project is marked as "retired" at BS, then the project stats for that host will drop off.
Just a note, if you have a lot of hosts, then trying to keep them all together could become a full-time job with endless frustration... Been there, tried that.
