Come to think of it, while doing this I found that the v1.9 branch was still intact, as were previous major revisions, so this fork is not even necessary. If anyone wants to contribute changes to the v1.9 codebase they can execute the same command:
hg up -r nopCommerce1.90Legacy maintenance changes can be proposed in isolated forks in this manner.
Derp. My bad. Deleted fork.
And to anyone who stumbled upon this and is completely lost, the CodePlex repository still has v1.90 as well as v1.80, etc. Just execute the command described in bold above from a command prompt (with TortoiseHG installed).
Standard Merc / CodePlex conventions likely apply. If you want to make contributions to a legacy version, create a fork
here, clone from the fork, execute the command listed above, make the changes, commit the changes (Mercurial
commit), then
push (Mercurial
push) the changes back to your fork, and if the core devs might want it in the mainline you can invoke the
request pull command from your forks' list on CodePlex.