Is it safe to break an aspirin into smaller pieces.?

A scored: aspirin can be broken along the score line. When cutting smaller than that - it is difficult to cut in to sizes that correspond consistently with a particular doseage.

Possibly: If the aspirin is uncoated, it can be safely broken. However, some aspirin tablets are specifically coated to prevent them from dissolving in the stomach (enteric coated aspirin); breaking those would jeopardize the stomach lining.