How do I switch between WLED presets and Artnet control without rebooting the whole thing?

No power cycle needed. WLED has realtime input handling built in, so when Art-Net data stops arriving, it drops back to whatever it was doing before, usually after a short timeout. Check the Sync Interfaces section of the config. There's a realtime override setting there, and you can set the timeout behavior so the strip returns to the last preset once the incoming stream goes quiet. That's the behavior most people want: presets run on their own, your laptop takes over when it starts sending, and then the preset resumes when you stop.

One thing to watch: if your lighting software keeps sending data even when you think it's idle, like a black frame loop, WLED will think it's still under realtime control and sit there doing nothing. Closing the show or stopping the output in the software usually fixes that. Some folks also just send a preset change command over HTTP to force it back, but in practice letting the timeout do its thing works fine. As for both listening at once, they don't really blend. When realtime data is coming in, it overrides the internal effects completely. WLED isn't mixing your preset with Art-Net, it's one or the other. The incoming stream wins while it's active.

On the IP thing, either approach works. Reserving the address in your router tied to the board's MAC is the cleaner option since everything stays in the DHCP pool and you don't have to remember what's taken. Or just set a static IP in WLED's network settings, something outside the DHCP range so the router never hands it out to something else. I've done both and honestly the router reservation is less hassle over time. Either way, once the address stops drifting, your lighting software will find the node every time. Worth setting a hostname in WLED too if your software can find it by name, that sidesteps the whole problem.

I've been testing this out myself and I'm glad the timeout thing works. When I leave the Artnet stream running for a relly long time, I noticed the main board seems to get quite warm. It wasn't hot enough to be scary, but it definately feels like it's working hard. Does switching back and forth between using the presets and the computer input put a huge strain on the chip over time? I just want to make sure I'm not going to fry it.

I've found that if I tweak the Artnet update frequency just a bit lower, the board doesn't feel nearly as warm during long runs. The latency difference isn't huge for my personal use case, but it's definitely noticible in terms of thermal management. Curious if anyone else has messed with that setting to save juice or keep the chip from getting too hot? It seems like a small tweak can make a big difference when switching between presets and external data.