I'm the other co-founder.

Yes, about as easy as opening a laptop. Unscrew some screws, lift a cover, install a new M.2 SSD or whatever. This is a picture of the "standard" assembly: https://i.kane.cx/NFIpf4 -- compute element slots into a connector, and there's the standard M.2 slot etc. Ours won't be too different, just a different form factor/connectors/additional features.

We're committing to selling all custom parts for at least a few years, but I can't give a hard number on how long. I'd say 4 years for sure.