FPGA can be programmed to do (almost) anything you want them to do.  You can reprogram / repurpose them to do whatever you want them to do, if you know how to do such things.

An ASIC only does whatever the guy who designed it told it to do before the factory built the chip.

There is nothing stopping somebody from releasing updated bitstreams for already purchased FPGA hardware that would allow them to do a different algorithm.  But nobody has done that yet.
There is not any technical reason preventing it from happening.

Whether or not they would have adequate performance is a different topic.