Yes, then the alimony is modifiable except as to what's outstanding. Sorry.
However, he's just giving amounts that he wants to pay.
He certainly can't just stop paying or he'll be in contempt of a court order.
Your going to go through a spousal support evaluation. Do you have any of the information from the prior determination of alimony - if so, get out that information and use it at the hearing. Just because his finances changed somewhat shouldn't affect your alimony payment - actually, to the contrary, he made the decision to chaange jobs and therefore should take the risk of the job reduction in pay. You didn't ask for more alimony when he was making much more money (that's your biggest arguement against any modification).
Also, gather up all your expenses, medical costs, anything and everything that you pay for this past year - use that also so that the amount stays the same.
Additionally, make the argument that the alimony was for life - that was court ordered - this is just retaliation of a poor choice on his part that you should not be responsible for.