Yes, you can use canned corn instead of fresh corn, but it will not be as sweet and crunchy. You can also use regular tomatoes and chop them, but the salad will not stay fresh very long. It's just fine if you serve it right away.
You can also add some cooked chicken to the salad.
If you don't eat the salad within a few hours, I always like to freshen it up with a bit more olive oil, red wine vinegar and dry herbs. Since the pasta will absorb the vinaigrette as it stands, it's best to add more later so it doesn't taste too dry.