If you want to hex edit, it's probably in the beginning of the file. Look for the previous value and try changing it.
I prefer to change the save type in the simuconf.tab to xml as it's easier to change the values.
Huge, huge, no even more than huge thanks for putting me on the right track.
Saving the savefile in xml was the easy step.
Save size did slightly increase indeed (size became 4.67GB)
Then opening the file with an xml editor.
At first no clue where to look for. Till I got the bright idea to start with a new save and use a rather peculiar value for the intransit value.
When I could locate the intransit value I thought I knew what to change (some boolean value from false to true)
However saving the file did work but opening in Simutrans didn't. As save size had shrunk to about 700MB I thought the xml editor was to blame
Found XML Validatorbuddy which is able to open rather large files. And behold I could save the file and open it in Simutrans.
So far no real progress with the amount of goods in transit so I decided to experiment a bit with the value. And yes it works!
Due to having a rather large map (4096*4096) and slow transit for some goods (ships) I decided to settle for a value of 2000. And yes, more goods are finally on their way.
So, save saved. Altered save method back to compressed and opened and saved once more.
So once more; thank you very very very much.
(Note: don't try this at home if your computer is not up to the task. I'm lucky (crazy?) enough to have bought a new computer this year with quite some memory)
I'm happy now.