Can maintenance be increased or reduced later?

Yes. the court may modify the maintenance amount if there is a significant change in the financial circumstances of either party. Life circumstances change, and the law accounts for that, Section 25(2) of the Hindu Marriage Act allows either party to go back to court and ask for the maintenance order to be modified, increased, reduced, or even cancelled, if there's been a genuine change in circumstances, like a job loss, a big raise, or remarriage.