In Notepad++, go to Language>Define Your Language>Import and select the file. Then go to Language>Event Assembler to enable Highlighting for your current file (It also automatically applies for newly opened .ea and .event files).
Necropost time. Here’s a dump of what I use for notepad++ syntax highlighting for EA scripts, thumb source, and textprocess scripts. They’re probably best optimized for dark mode.
Disclaimer: They’re custom made by me, and intelligent design in any regard is not guaranteed in any way, shape, or form. There’s also a bunch of stuff (macros, etc) that are useful probably to me only.