I dought anyone with DP that has any sense left will do DXM in any form. And if they do, they shoudnt complain about their DP getting worse.
Yes i would recomend anyone who has depersonalization or derealization to stay away from DXM (unless you take it in low doses used as a cough suppressant but it is near useless for this purpose so it's hardly worth it) or any other dissociative. Atleast if your dp/dr is active anyway but even in remission you take a risk. This excludes dissociative anesthetics used for medical purposes such as nitrous oxide or ketamine used during certain procedures of course.
Basically all i was saying in that post was that if you do go ahead and try DXM to get high make sure the only active ingrediant in the product is dextromethorphan. Anything else and you risk alot more then making your dp/dr worse. You run the risk of death while having a awful trip when you either OD, have something go wrong with your heart or have a stroke. Or even worse you die a slow agonizing death due to acetaminophen/paracetamol poisoning. That would have to be one of the worst most painful ways to die.