Hi all, using 2.5 is it possible to insert "invisible" operations, that are operations I would like to track but I don't want to be considered as cumulative in the total, report, and so on?

No, this is not possible.
You can create operations associated to a tracker.
Then, in dashboard / report, you can choose the options to not take into account operations associated to a tacker.
But, these operations are in the totals of accounts.

What do you want do that? What is the use case?

Up!