Is there a way to have your 240 central ac unit circuit double as a regular outlet in winter time for use in christmas decorations
What you could do is install a small sub panel at the end of the wires. Install an additional 240 volt breaker, same amperage as the breaker feeding the AC unit and a 120 volt, 15 or 20 amp breaker for the outlets. This requires that you have 4 wires feeding it, two hots, a neutral and a protective earth. If you only gave three wires (no neutral) you’ll need two 240 volt breakers and a step-down transformer to get the 120 volts.
You would need a converter to go from 240 to 120 and then you could.
Check out this post Replacing 240V outlet with 120V. It'll give some ideas.
The circuit protection device for your AC unit will likely be way too big for protecting small things like decorative lights. That would have to be changed, then changed back again when you want the AC again. Not worth it...