Can the constitution be changed without changing the Constitution? Well, yes. Obviously. The Supreme Court can change an interpretation. Congress can establish procedural rules (frex, the filibuster). And states can alter the way they select electors to the Electoral College.
New York state just approved the National Popular Vote Interstate Compact, which commits states that sign it into law to allocating their electors to the winner of the national popular vote rather than the winner of their state election. If states sign on representing a majority of the Electoral College (e.g., 270 electoral votes) then the U.S. will fundamentally alter the way it elects presidents. Here is the current state of play:
Note that only blue states have signed on. Why is that? Well, I don’t know, but here’s my guess. A national popular vote would behoove both parties to try to mobilize voters that are currently ignored in non-swing states. Republicans would try to turn out conservatives in Wisconsin and New York; Democrats would go after liberals in Texas and Georgia.
Democrats are pretty sure that there are a lot of untapped votes in deep red states. I am not sure that Republicans believe the same about the blue states. But I do not know! Thoughts?