Switching is what you call it when you take someone else's jokes, modify them and use them. There's a line between switching and plagiarism. Some gags and plots are more switchable than others. Never, EVER switch a joke from Reader's Digest or Boys' Life. Making events happen on a really big scale doesn't make the series better.
Comic strips can be small or large.
I recommend that you make sure you've got a good joke to go along with it, rather than just a mention of another strip, before you run it.