You can run individual scripts with node by using "node path/to/script.js". When you run "npm run upload" you're actually running "node _functions/upload-neo.js".
You could move that script to another node project, but you'd have to tweak it since it's designed for strawberry starter (specifically, it checks for a config.jsonc file in "src/_data" to check for a subdirectory, and it reads a folder named "_site" to check what to upload.) You'd have to initialize a new project with "npm init" and then install the script's dependencies with "npm i form-data jsonc". That's overkill if your site isn't already a Node project, though.
However there's a Neocities Command Line Interface that lets you upload your site from the command line. It has a different syntax and some quirks but fundamentally does the same thing - only uploads what's changed. This is the best way to go about uploading things if your site isn't already a Node project, I think! I would use that tool to upload your base site and use npm run upload to upload the blog.
yay!