Dear Tim:
Should a person have two bridges? And should they change them themselves? How can you tell if your sound post is in the right place?
The professionals often have two bridges, one for winter, and one for summer. I wouldn't make it a high priority, though.
You can change your own bridge, but be sure that the sound post doesn't slip out of place, or your cello could collapse. The sound post is not only for sound transmission, it also acts as a structural support. There's a lot of pressure put on the cello due to the tension of the strings, which is resisted by the sound post.
You need to bring your cello to a repair shop to have your sound post adjusted. The repair person has special tools for this. He or she will move the sound post around until the sound is optimal. You can't just play your cello at home and determine if the sound post needs adjusting. Like getting your car tuned up, your cello needs one every year too.
Tim Janof