Can you convert a wood burning fire pit to a propane burning fire pit?

Just about anything is possible. There are certain enviromental and safety factors that have to be considered. If you live in a northern climate, northern U.S. or Canada, the fact that the ground freezes and thaws every year up to 4 feet down is a major concern b/c that would cause any underground gas lines to possibly heave and break or leak. Also, a gas fire pit has to be properly built and weatherproofed to avoid the exposed metal gas nozzle from coming in contact with water which can cause corrosion, or, water in or around the line freezing which can cause a break or a leak. The best thing to do is to research custom landscape companies in your area who have done proven, quality work like this in the past. Talk to the city to see if you are allowed to build it in the first place. They can make you tear it out if it is built without a permit, or not done up to code. Next, talk to the local gas company to find out what is the best piping system to use underground in your area. If you're just going to build it yourself, do all the research you can, plan it out completely, and don't blow yourself up.