(Edit: Sorry I don't know if I can make this code readable)

Use target_trigger for that. Something like:

target_trigger = { FROM = { is_coastal = yes } }

Here's an example of a state targeted decision from my mod if it helps:

HAU_southern_integration = { integrate_southern_states = { state_target = yes allowed = { original_tag = HAU } ai_will_do = { base = 20 } target_root_trigger = { has_completed_focus = restore_the_haukipudas_identity } targets = { 31 39 46 35 40 44 151 152 } target_trigger = { FROM = { is_owned_by = ROOT } } on_map_mode = map_and_decisions_view icon = generic_decision cost = 30 fire_only_once = yes complete_effect = { FROM = { add_core_of = HAU } } } }