Raising your MAX HR?
 

Is it possible to raise it with training or will it either lower or maintain itself as time goes by?
Also, what is the effect of training on my max HR on the long term, will it maintain it or just slow the decrease?

Meth, cocaine, or some incredibly powerful narcotic is about the only way I know increasing your max HR. It would also be temporary, and extremely hazardous to your health.

Your max HR is sort of a fixed thing from what I know, and has a tendency to drop slowly as you age.

If I'm wrong, someone please correct me.