What do you mean by "node"?   You can reserve IP address for a device.   I did it with my Hayward Pool control as I need to access it using IP address on my browser to control the pool, so I don't want to keep changing my bookmark whenever the power went out.    I don't know if it actually works or not as I have not unplugged the router after I reserved the IP for it.   I guess I will find out next time when power goes out.

Or node means the "Linked Deco" device?   You want some of your devices to only use one of the 3 Deco and not the other ones?   There is an option under each device connected turn OFF "Mesh Technology".   It said under it:

Disabling this option will turn off seamless roaming between Decos for this device.

  @lostchild Thanks.  Yes, I mean "linked deco device" (AKA any device that's not the 'main' one.)  Unfortunately, my experience with another Deco model and several posts here confirm that the "disable mesh" option doesn't always work the way it's described - whether that's a Deco issue or an issue with the connected clients I can't say, but that's the reality that I and others have observed.

My exact situation is that even with my current (X68) model, even having a dedicated 5GHz backhaul band still results in significant signal loss, even in a tiny house, and even when the satellites are tested in the same room as the main.  I basically only need them to function as extenders for my 2.4 GHz cameras outside the house, but my other 'important' devices always seem to pick up the weak 5GHz signal from the closest Deco (as is the point of mesh), but the signal from the main is signicantly stronger, and I'd like to force these to always be on the main.

I read another reply somewhere from a TP-Link employee that they're working on firmware to enable a separate IoT 2.4 mesh network, which would be really nice, but honestly I'd like to disable the 5GHz mesh altogether and simply use my other linked Deco devices to extend 2.4.