OK more research findings.
According to TRENDnet my TEW818DRU router is "
DD-WRT compatible". This came to me as somewhat of a supersize, and not knowing exactly what it meant, I decided it was worth a call to tech support. Long story short, the DD-WRT firmware has to be installed before the regular Trendnet firmware, whereupon the warranty is nullified, and tech support is no longer available. Never having used
DD-WRT I still don't know if this enables the multiple VLAN objective, but it sounds like it is in the right direction.