I’m almost 55 and have been training off/on for the last 30 years - my diet is pretty dialed in for maintenance and my workouts are mostly full-body, 3 days a week with some variation every 6-8 weeks - I wanted to bring up my shoulders a little by hitting them with more volume; changed up my routine to hit them twice a week with a combination of low/heavy and high/light exercises and set/rep scheme - I know its generally difficult to spot reduce but is it possible to bring up a lagging body part with minimal diet changes? I understand basic building principles; you have to increase calories to fuel muscle growth, but for very specific, targeted training on a body part, particularly shoulders (not something like legs or back), is it possible to stay in mostly maintenance calories and see some progress?
I think you could def bring up shoulder in this manner.
IMO for shoulders you would increase only side delt work. Rear delts usually get enough work on pull days and front delts get a great deal from chest movements.
Can you post some pics so we can see your shoulder muscles distributuon?
Increase frequency of targeted areas. Focus takes focus, so don’t worry if your shoulders are growing but your deadlift is stuck, as long as any compound lifts are being done at a normal weight and once or twice weekly.
Think of full body workouts as maintenance, so do don’t try to advance on those lifts. You can let them passivley increase by consistency, or can spend 6 weeks to a year bringing up stuff and lit it ride.
Keep nutrition the same. Your auto-pilot baseline is what keeps you where you are.
Increase pre/intra/post nutrition on specialized days. Punctuated equilibrium is relevant to growth.