2 things I've found...
I would add a sentence stop at the comma here. Otherwise, this whole paragraph consists of only one long sentence. Instead, it would read like this:
It is also possible to specify a date. In that case ... last true commit.
Don't forget to add an extra space after the sentence stop.
If I remember my school english correctly, there is something missing here (*looks to native speakers for help*). I think it should say:
If some files have been added, or were removed during ...
I don't want to judge about the grammar as I'm not a native speaker, but what the change tries to say is what I was misunderstood when I struggled while resurrecting a port in the first place.
The meaning of "last true commit" is kind of unclear.
The use of "Perform whatever" is a little weird. How about:
Make the changes necessary to get the port working again.
Needs a comma at the pause, and avoid using "you":
distfiles are no longer available, either volunteer to host the distfiles, or find someone
"appropriately" must be interpreted by the reader. It would be helpful to expand on that, like "to make sure the source control tracking of those files is corrected." (There's probably a better way to say that.)
End the question with a question mark.
This should be "for doing so", but is not really needed:
merged, and respond with the proper procedure.
No comma after "number".
This can be reworded into a smoother sentence with less pauses:
A script is provided to automate merging a specific commit:
Passive->Active: s/It can be/It is/