There is not. ViewSonic, for whatever reason, builds their projectors in such a way that QLab literally has no way to tell one from another, so even if you could add your own label, there’s no way for QLab to be sure it would apply the right label to the right projector after a reboot. This is a limitation of the projector, unfortunately.
The best way around this is to use an EDID emulator. The Atem VC080 is an example, but there are others. They plug directly into your Mac and pretend to be the display, and many of them like the VC080 can be manually programmed with a unique name.
Best
Sam
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Sam Kusnetz (he/him) | Figure 53