Actually certifications doesn't change from month to month, they change roughly every 3rd year. The way this currently works is that when you pass a certification it's valid up to a year after the next update of that certification (this cycle is roughly 3-4 years).
If you wanna be a certified developer you typically have to pass a certification every 3rd year to maintain that status.
Anyone can be certified in any area. However, Microsoft recently changed the way certification and partner status work. Previously, you just needed a certain number of certifications within your organization, today you need a minimum number of certifications within a specific area to attain a higher partnership status in that area.
This is interesting because organizations which value certifications will look at what type of certifications you have in order to maintain their own status within a particular area. If you wanna be certified, I'd recommend looking into the areas where you wanna work. Those will give you the best outlook.
You should also consider that the entry level MCTS certifications are broad and test a wide range of know how. If you have lots of experience you'll likely find MCTS very easy, but if you don't study correctly, you'll likely fail the MCTS exam. The overconfident ones that try and head butt their way through the MCTS exam are typically the ones that fail.
There's this company called MeasureUp that provide on-line training and tests that you can do. These tests will give you an idea of what it means to pass a certification. I believe there are some demoes you can try out yourself without having to commit.