Can I move or redesign the interior (partition) walls in my contest proposal?  
Yes, you can move and redesign the partition walls. You can’t move the entrance door, the balcony door and the windows.

Is the interior space height 2.70 m (standard H)?
The maximum height is 3 meters (see this info in the dwg file you can download from the WFH2020 rules)

Is it possible to demolish the walls composing the bathroom and the bedroom, as from the layout you provide and freely decide on internal walls and the placement of the drains? 
Yes, internally you can demolish everything. What remains fixed is: the entrance door, the windows and the balcony door.

Registration and payment must be done by June 8th, the same deadline for file uploading?
Yes, registration and payment must be finalized by June 8th, whilst files must be uploaded by June 15th. 

I wanted to ask what the interior dimensions are. To verify, is it a 8.6m x 7.2m floor plan?
Yes, the dimensions of the floor plan are 8.6m x 7.2m

Since the external walls, the windows and the doors cannot be modified, can the balcony/terrace area be used for another function? Or should it be considered as it is, at the service of the rooms, assuming this accommodation is part of an apartment building complex?
The accommodation must be considered as a housing unit of an apartment building complex, for this reason, “structural” changes in the balcony/terrace area are not possible, but different functions can certainly be identified.

Regarding the file, you provide: is the terrace projecting from the wall or not? And above all, would it be possible to have measurements of the height of the openings from the ground?
The terrace is aligned to the wall, as in the dwg.  Height from the ground: 90 cm (the height of the frame is 140 cm).  French door height: 240 cm

Regarding functionality: do the two inhabitants of the apartment (“Roberto and Giulia”) work from home simultaneously only for a few days of the week or alternating with each other? The expression “every other day, as it is written in the competition rules, is not clear.
The inhabitants of the apartment work from home on alternate days: for example Giulia on even days and Roberto on odd days.

Should the exterior wall of the balcony remain white? Or is a cladding design allowed? 
Yes, a cladding design is allowed