Hi Tumbler,
The engraved screws are usually quite soft so be very careful. Using heat from a soldering iron is a good idea to help loosen them but try not to destroy any heat coloring originally applied. Be careful about scraping away any varnish unless you are absolutely sure it is some later addition. The steel hardware was likely charcoal blued and sometimes a varnish was applied over the metal to preserve the color, which can fade over time. A light cleaning is not a bad thing but too vigorous and it can ruin details and destroy historical value. Hopefully, you don't plan to re-brown the stub twist barrel. I assume there is one lock bolt. The lock almost certainly has a hook or lug on the front that catches a stud imbedded in the lock mortice. Be very careful removing the lock. Loosen the bolt and then tap it gently to push the lock out. It is going to still be caught in the front so it will come out at a slight angle and may snag brittle 200 year old wood
along the way. Just tap a little, inspect, tap a little more, inspect, etc. I also recommend placing the lock at half **** and engaging the sliding safety bolt before attempting to remove the lock. Over 200 years of age and wear may allow the hook on the mainspring to drop a little lower in the mortice possibly snagging wood on the bottom. By placing the lock at half **** before removing, you should avoid that risk. If you clean the checkering, use a soft brush because 200 year old wood can be brittle and you could chip off a diamond.
dave