Hello there,
I am planning to develop plugins for commercial use. My question is:
is it legit do anything I’d could be able to do? For example, little hacks and tricks in user interface for modify native behaviours that current platform doesn’t allow to modify?
and exists some documentation talking about this?
IIRC, Atlassian only slightly cares about copyright/trademark infringement (mostly in regard to her own products, with examples focussed on naming and use of logo’s) and obviously about ADPR (Atlassian Data Privacy Restrictions, as I call them given that they are a unique interpretation of GDPR). Which means that you cannot mess around with customer data. Also, in Cloud, Atlassian has restricted a lot of things apps can do, forcing some to create browser extensions to do the things you’re suggesting.
Apart from that, all bets are off. You’d still have to convince the customer though, so it’s probably good to be transparant about what you’re going to do to their systems.
Thanks for the reply remie. Let me show a imaginare example (I don’t even know if this is possible):
You want to add a screen in approval/reject buttons in customer portal. You can’t just add a screen to your transition because it is ignored. But you can write a plugin using javascript that hooks the Approve/Reject button and show a modal dialog. I guess that’s not the best way to do that, and maybe there is no alternative. In that case, is it legit?
It is legit if the customer agrees to it. As long as you are straightforward in what your app does, and how it affects the user interface, performance or customer data, you should be fine. I would personally recommend that you add an EULA in which you specify that the app makes adjustments to the native experience and that you cannot be held reliable for any damage that might occur because of it 
The customer is required to accept that EULA prior to installing the app.