The original technique of increasing the size of the img file using truncate, apparently used to work.
Note, there is no need to resize the working-partition to fill the extra space -- easyos will automatically do that.
This evening I have installed ventoy 1.0.89 to a 64gb usb-stick.
I increased easy-5.0-amd64.img to 4gb and copied it to the usb-stick 1st partition.
Booted the usb-stick, got a grub menu, with easyos listed, choose it, but then lots of errors flashed by.
Managed to see one of them -- it seems wants the easyos linux kernel to have device-mapper (dm) support.
Hmmm, is that a new requirement that ventoy has introduced?
The easyos kernel does have dm support, but it is a module, only available after the initrd has finished.
Right now I'm compiling kernel 5.15.99 with dm support builtin.
Will build easy with that kernel and try again.