This "may" be a bad idea. "Sometimes" the additive packages of different oils don't chemically get along.
The chemical engineers at these companies did a lot of work to figure out the concentration of each additive in the add package of these oils, and backed that up with spending a significant amount of money and time actually testing these oils by running engines using them.
People that mix oils are basicly throwing all this research work out the window and taking an unknown shot in the dark by mixing something up.
Lake Speed has gone into this on his YouTube videos. It's a really bad idea. Just don't mix oils.
Formulating good motor oil may not be rocket science, but it does require very intelligent people who are very knowledgeable about all the additives and how they interact with each other.