If you want to up or downregulate a specific receptor the key is not targeting the receptor itself

Instead, alter the receptor expression using kinase activation, or alter the function of its transporters either directly or by changing epigenetics (methylation, acetylation, etc)

As an example let's look at the glutamate receptors, specifically the NMDA subset, which cause excitotoxicity

They are particularly difficult to downregulate as they change very slowly, and you can't use anything that binds to them potently without risking seizure/toxicity

Instead, you must target factors that will influence them indirectly

One way you can do this is through activating the kinase TrkB, and the simplest way to do this is by increasing its primary ligand, the neurotrophic factor BDNF (using supplements like magnesium, bacopa, etc)

If you want to alter the glutamate transporters there are many supplements that increase them directly, more transporters = faster glutamate metabolism

Factors that increase the primary transporter EAAT2 include: omega-3's, NAC, zinc, skullcap, harmine, magnesium, and lemon balm

Other pathways that increase glutamate transporters are listed here, you can achieve the same effect by axtivating a few of these in some cases

With any supplement evaulate its complete effects, some may have negatives that outweigh any specific benefit or have interaction risks