+1 I've often wanted to change one or two default values in bootstrap, such as the primary color, but can't be bothered to pull it locally and rebuild it. I'm not aware of any sites that do this for me, would happily pay $5 or $10 once for a web tool where I could make these changes (just list all build variables) and save configs
I think front-end devs forget this part, because they always tend to have a giant complicated built tooling setup in place, so adding one more little thing seems easy.
But the default is to have no tooling whatsoever, so the thing you're proposing that you "don't know what the problem is with" is a process that has a step one that lies several steps before even "install Node on my dev machine".
I've gone through all that (specifically to change a color in bootstrap), and even now that I have it set up and runnable, I'd still use the grandparent's proposed $10/month web service if it existed.
Edit to add:
...and now that a sibling comment has pointed out the existence of bootstrap.build, I'll be signing up for a paid account.
