"On front axle, decoupling target meets but what will be imoact on decoupling of powertrain mounts on rear side?"
I don't understand what you mean. Explain to the rest of us what The Big Picture is. What are you trying to do, what are you trying to build, and why?
I am going to ASSume that you are using a rigid front axle and front differential assembly such as that found on heavy-duty trucks with 4 wheel drive (for example, Ford F350 Super Duty). If not ... explain.
Front axles are designed to have steering mechanisms. What do you want to do with that, if you want to put this axle on the rear of a vehicle? Are you designing for 4 wheel steering?
Front axles can have locking hubs to allow them to be decoupled, whether manually or automatically. If that's what your axle has, its function will be retained. If you unlock the rear hubs then you're no longer driving those wheels. If those are the only wheels you're driving, you are now stuck without being able to move. It won't break anything ... you're just not going anywhere. You can get axles without locking hubs that cannot be uncoupled.
Front axles on that type of truck generally have the differential off to one side, in order to clear the powertrain in the middle of the front of the vehicle. When moved to the rear, that's going to put the drive shaft off to the side, and that's going to necessitate having the powertrain off to the side (and this is ASSuming that the chassis allows for this to be done). Is that what you want? Is the asymmetrical weight distribution going to be a problem? If the powertrain up front is not in the middle, is clearance for front wheel steering going to be a problem?
And yes, the rotation will be the wrong way 'round unless you also flip the axle upside down, which they're not designed to do. Things that will be wrong: vent hose too low, fill plug too high, steering knuckle geometry wrong, probably loading the steering knuckles the wrong way.