It all depends on what you do!

Coming from a naive position (as I’ve never made this customisation before) my thought is that you would need to change the way the service operates so that a file is uploaded on submit to a part of the account’s file cabinet

So it would require changing not only the frontend modules but the backend ones too

So “how risky is this?” well, you’re potentially changing an entire group of modules, either by replacing/overriding them or by extending/wrapping them. When the source bundle automatically updates you could be in for trouble if we ever do something that messes with the fragile away you’ve applied your customisations

My only other thought was to create an entirely separate ‘file upload service’ that uploads files completely separately from the rest of the quote and then attaches it later on, which might be less fragile but more work

But I’m not an expert on these kinds of customisations 😄

that is a good suggestion