Can I choose the image size exported to the feed?

To do this, add a replacer that will add the appropriate suffix to the image link, e.g. we have the URL:
https://demo.presta.show/demo/dcgts75pbcib/img/p/2/2.jpg
so we add the modifier:
/^(.+)(\.[^\/]+)$/
and set it to replace with:
$1-large_default$2
below is an example shown in screenshots: