I have a 8 thread CPU (7700K). I'm running BOINC and also Folding@Home, prioritizing Folding@Home over BOINC right now.
Since Folding@Home have shortage in work units, I want to allow BOINC to run when some of my CPU resource is not used.

So I think of configuring BOINC the following way:
IF FahCore_a7.exe AND FahCore_22.exe are running THEN suspend.
IF FahCore_a7.exe only is running THEN use 13% of my CPU.
IF FahCore_22.exe only is running THEN use 88% of my CPU.
if neither process is running THEN use 100% of my CPU.

Is there a way to configure BOINC that way?

Thanks in advance!

No, that is not possible. It isn't possible to set parts of the CPU (cores) to do work when "demand must be met".

---

What I would do, is assign 5 to 6 out of 8 cores to FAH, and configure Boinc to run 5 to 6 cores.
That means that either project will run at least 4 WUs at normal speed, and only runs 1 to 2 overlapping with the other program.
Meaning when FAH has jobs availble, you should get only a small performance penalty.
But when they're not available (and you're running between 0 to 2/3 cores on FAH), Boinc will run the remaining 5/6 cores at full speed.

There's no dynamic adjustment possible, since you'll need to restart the service when you update the "global_prefs_override.xml" file.

It would be interesting to see if it can be adjusted dynamically from terminal, since Boinc Manager does it somehow.