Update only stock of existing products csv file

Thank you very much as always Nicolas,
I have tried point b) and it works correctly and it has helped me a lot.

Regarding what you tell me about: "That way, if you run these mass actions one after the other, you'll have what you want.
The problem is then automating that, if you need to do that task periodically. Because there is no mechanism to set an order on the mass actions, or to say to run another mass action after one. That would require a bit of coding."

It's what I wanted to ask you about later, but since you bring up the subject I'll tell you right here. Perhaps what I am saying does not make sense, but I would like to know if the following can be done:

It is to put at the end of each massaction a Run SQL query that unpublishes the current task and activates the next one, in this way the massactions could be ordered and then the frequency of the cron could be played with.

Would this solution be viable, if so, could you tell me what the sql query would be like to perform some tests?

Thank you very much again and best regards.

Thank yoy Nicolas, it works perfectly!!!