Listen to USAFRet says. I think the question in itself makes little sense because if you have personal and important files stored, you have to take into account the hdd can break down at any moment.
When that is said, yes - for many hdd models it indeed is possible to lengthen the expected lifespan. I don't exactly remember the term for this, but hdd's have a setting that controls how aggressive/fast the head moves, mostly for A - reduce sound, and B - getting down search time. This settings also have an affect on the hdd lifespan - at least in theory.
Another factor to consider is the number on power on/off. The numbers of running hours for a hdd should be optimal when it turns on and stay on for the rest of its working time. But for a home user that of course is less likely anyway.