How to add an additional MQTT topic/attribute to Climate entity

First, MQTT ignorant. I have an Omnilink Server (which interfaces with an OmniPro panel) configured with Mosquitto. The Omni thermostats have a ‘Hold’ feature which stops it from changing the temp based on the programing. Nice to have when you’re heading to Florida for the winter. In Mosquitto, it’s topic(?) shows up as hold_state. Is there an easy way of adding this attribute to the Climate entity so it’s accessible in HA? Further, and of less importance, I can’t figure out how HA attributes like current_temperature_topic gets mapped to the corresponding Omnilink attribute, which in this case is current_temperature.
Thanks for any help.