I have a 2015 Salsa Vaya 2 with a Shimano 105 drivetrain. It has a Shimano 105 Triple front derailleur with a 30/42/52t crankset. In the back it has an 11-30T 10-speed cassette (installed for me by the LBS instead of the stock 11-28T one). I was told at the time that I can't get a lower-geared cassette on this bike.
Now I'd like to get into some light touring, and want to lower the gearing for climbing with load. What are my options? I see some 105 cassettes with larger big cogs (e.g. 11-34 11-speed). Can I just drop one in? Do I need a different rear derailleur, a new shifter, or any other parts to ensure things work?