I think I'm about to set off on a project which will have a lot of mesh gradients using colours drawn from a relatively limited palette.  So let's imagine I've got a few dozen mesh gradients in a picture, all using colours drawn from the same palette.  Would there then be a way I could experiment with how it looks using different colour palettes?  I.e., changing every instance of a particular colour(s) that I might have used in all of the mesh gradients?

There is the direct approach -changing the colours in the svg all at once. 

It can be done with notepad++, then you'd need to save in notepad++ and revert in inkscape. 

Maybe not so convenient, but it works. 

Haven't tried, but maybe you could turn your palette into swatches and by using those swatches it could be changed globally at once. 

In the late forum Ragnar posted a few extensions on the matter.

Other option is using a filter for gradient mapping. 

If the mesh gradient is greyscale, the luminosity levels can be mapped with any colours defined within a filter.

With that approach making small changes is easy after the initial setup.

Thanks very much @Lazur, I didn't realise I could just edit the svg in notepad (I'm new to this).  That will be a perfect solution for me.  :)