In Washington, spousal support, also known as alimony or maintenance, is modifiable under some conditions.
First, the decree of divorce must have NOT ordered non-modifiable spousal support. Second, there must be a “substantial change of circumstances”. I would add, however, that in my experience, spousal support modifications tend to be disfavored by the courts (i.e. you need to have a VERY good case).
Sometimes couples in a divorce will agree to make the maintenance obligation non-modifiable. This is generally because they value certainty over flexibility. When the support is non-modifiable, then the paying spouse knows the other spouse cannot go back to court to ask for more support, and the receiving spouse knows the other spouse cannot go back to court asking to lower support.
If the support is not specifically ordered as non-modifiable, then it is modifiable.
However, the support can only be modified as to future payments, not past payments, and modification requires a showing of a “substantial change of circumstances”. This means that something must have changed significantly since the support order was made, and the change must have been one that would not have been reasonably contemplated at the time the order was made.
In other words, it must be something very unexpected, such as developing a long term illness. Simply losing a job would likely not be enough, unless it could be shown that there was no ability to find new work with a similar income (for instance if there have been unanticipated industry changes).
It should also be noted that unless the support order provided otherwise, the support obligation does terminate on the death of either party, or on the remarriage of the receiving party. However, the former spouse merely cohabitating with another party is generally not a sufficient basis to have support modified.