Yes, you can, though there will be less tension in the strings which can be problematic in some instruments where string tension affects the instrument's rigidity.

The weight and thickness of strings affects the way they vibrate. Tightening a thicker/heavier string compensates for this, but there are limits. Similarly, a lighter/thinner string will need less tension and there will be a point in either case where either the string snaps or there is so much slack that the string vibrates against the neck/frets.

There are ranges of strings available for guitars - from extra light to extra heavy, so buy some cheap ones and experiment as to which ones suit you the best.

Hope this helps

CamoJohn