There's a go edit -replace command to append a specific commit (even from another forked repository) on top of the current version of a package. What's cool about this option, is that you don't need to know the exact pseudo version beforehand, just the commit hash id.
For example, I'm using the stable version of package "github.com/onsi/ginkgo v1.8.0".
Now I want - without modifying this line of required package in go.mod - to append a patch from my fork, on top of the ginkgo version:
$ GO111MODULE="on" go mod edit -replace=github.com/onsi/ginkgo=github.com/manosnoam/ginkgo@d6423c2
After the first time you build or test your module, GO will try to pull the new version, and then generate the "replace" line with the correct pseudo version. For example in my case, it will add on the bottom of go.mod:
replace github.com/onsi/ginkgo => github.com/manosnoam/ginkgo v0.0.0-20190902135631-1995eead7451