UPDATE / SOLVED WITH MY METHOD
1 - I've added to the project all the new bars/fixtures, configuring properly the new DMX address, according to my new expanded setup
2 - I've created a new scene, and in that scene I'm start to positioning and dimensioning well the new bars (in terms of fixture rotation, placement and size), but non finished yet completely
3 - I'm going in EDIT mode from that created scene, then I select all (cmd+A) all the cue/scenes, and then, very carefully, I've start to complete the perfect positioning for my setup: turning all "red" the "yellow" parameters, but absolutely not touching the "media" related section. In this way, all the scenes/cues mantain the original assigned media, but with a new placement of the bars/fixtures. Exiting the EDIT mode, now ALL the scenes/cue have the same new setup/position, but with the previous programmed medias.
4 - Scene by scene, cues by cues, I've turn on the new bars/fixture, already positioned, "simply" updating the values for each (add all).
5 - Done!
My personal consideration: I think it's a really bad & boring way to expand a LED setup, especially when you've already programmed over 50 scenes/cues with different medias... and this need to happen every time u need adding or modify the main setup... hope in the future there will be a more easy and fast way to do it. Or... just simply I've not understand the software

Hope this can help someone.
Greetings from Italy ! Fabio