MODx Revolution: Setup and workflow for testing changes before going live?

MODx Revolution: Setup and workflow for testing changes before going live?

I've searched around to find a tried setup that would enable us to test
changes before publishing them for the public to see. The nearest I've
seen was this question, but it seems to have died.
We're building a website with quite some user management logic, so the
question is mainly in regard to code, rather that html content; generally,
the changes that are likely to break bigger portions of the site, like
layout, backend php, and structure.
As there is a lot of logic, i.e. real code, I'd prefer to have the actual
content in files and versioned with git, and only include them in MODx via
static resources/elements.
I see that new resources need not be published to test them, but what
about changing resources? Can a (static) resource be changed and tested
while serving the old version?
Can/How can different development/production sites help with this?
Structural changes generally mean that resource IDs change, so files that
reference these IDs need to be changed before being moved into the
production system. Is there any way around this problem without
sacrificing the ability to test structural changes?
I'm absolutely fresh to MODx, so any of the assumptions I may have
communicated are up for debate. I just think that this makes it even more
important to be able to test changes before they go live.