I agree with everything Piscean has said above (in post #58). In post #55, I said that "great change over time usually implies a succession of little changes." I would like to clarify that that is just from a pragmatic standpoint, with cities in mind. And it is only with "normal" city change in mind (buildings getting built and so forth). I did not intend to deny the possibility of fairly instantaneous large-scale change to cities (via atomic bombs, tsunamis, and the like).
From a linguistic standpoint, however, it is clear that the verb "change" in "The city has changed greatly" refers to a (durative) process. Certain linguistic tests can be used to show this. For example, we can say, "
The city has stopped changing"; "
The city has changed (or been changing) for a long time." But it sounds very strange to say thing like ? "
He stopped graduating from college" and ? "
He stopped reaching the top" (which only make sense on a habitual reading). "Graduate" and "reach" are punctual.
The sentence "The city has changed greatly since 2012" is talking about the extent to which the city has undergone the process of change between 2012 and now.
'Change' can be be a momentary thing, as when a magician passes his hand over a king of clubs and it changes into an ace of hearts, but it is normally a process that can take a period of time, sometimes years.
It seems to me that (b) ("I have changed my address since last year") is a case of "change" being used punctually (i.e., in a verb phrase that represents the situation to which it refers as punctual). While it might take time to type an address into a computer, the transition from one address to another in a computer is instantaneous. I think that "He
is changing his address with the post office" can only refer to the preparatory phase, not to the transition itself, which the VP "change one's address" denotes.
In conclusion, I venture to assert that "The city has changed greatly since 2012" is durative and that "I have changed my address since last year" is punctual.