that depends on how much you know about electronics and soldering.. if you feel confident and you have tryied EVERYTHING, besides of taking it to nokia for them to test...
i mean, you NEED to be 100% sure it is a hardware issue..
and if you are out of guaranty or you dont care to loose it..

i guess you could give it a try.. after all... n900 IS a hacker's phone right ?

good luck with that, let us know how it goes. If you do change the accelerometer, it would be awesome if you could take some pictures and a walkthrough of the whole process..