Use set for multiple handles...
set(hL1,'linestyle',':')
Don't know why TMW didn't add the facility in the methods; if going to trouble to write them one would think they'd be useful for the real world cases, not just the simple ones.
doc set % for details
Drill down for the arcane cases of multiple handles w/ differing values, etc., etc., etc., ... You can do almost anything desired via cell arrays as arguments.