Perform merges when substituting dict keys (#3062)

esphome/components/substitutions/__init__.py

@@ -5,6 +5,7 @@ import esphome.config_validation as cv
 from esphome import core
 from esphome.const import CONF_SUBSTITUTIONS
 from esphome.yaml_util import ESPHomeDataBase, make_data_base
+from esphome.config_helpers import merge_config
 
 CODEOWNERS = ["@esphome/core"]
 _LOGGER = logging.getLogger(__name__)
@@ -108,7 +109,7 @@ def _substitute_item(substitutions, item, path):
             if sub is not None:
                 item[k] = sub
         for old, new in replace_keys:
-            item[new] = item[old]
+            item[new] = merge_config(item.get(old), item.get(new))
             del item[old]
     elif isinstance(item, str):
         sub = _expand_substitutions(substitutions, item, path)