Hi Michail, I don't have a multi-tenat QRadar SIEM available so I can't try excatly what I'm wrinting here.
What I do remember it's that you CAN at the domain configuration level, select which data it's part of a Domain, not only by selecting the log source, but only part of the data of a log source based on "Custom Properties".
Not sure if that will satisfied you requirement, but you could give it a try.
Just in case you may also upload your requirement to the IDEAS portal where the Product managers can review it an add it into the product:
https://ideas.ibm.com/products/7003354097537438773
best regards
best regards