Specifically this. Without being above-average proficiency with X, the format and available options are likely to be difficult to figure out.
> "GUI-based configuration is unnecessary", so how exactly is Alacritty easier than urxvt
The config file is well documented and in a human-friendly format. Most flags will also take effect immediately without restarting the program.
> One feature that I really miss in rxvt is an easy/fast way to change the color scheme, or at least reverse colors (like with xterm, which if correctly configured it's just ~3 times slower than urxvt). This is something really important when your screen receives direct sunlight.
You could have two `colors` sections in the config file and just uncomment one or the other. Not quite as convenient I suppose. One thing I'm considering as a key-binding option is to exec a command. This could be anything like `sh swap_config.sh` and then you could bind it to whatever you like.