I intend to buy a neighbour condo directly besides my current unit. I plan to hack the inner wall separating my unit and the neighbour unit. My question here is if this is allowed by the authority and is it safe to do so? Anybody here has done this before? Please advise on your thoughts.

AFAIK when we asked about this, some managements will allow for a doorway, but not a whole wall though i think it depends on how the building was built and the management's say in this

I am guessing AFAIK means As Far As I Know?

What concern me is whether do I need to get the PE endorsement and approval from local council kind of stuff etc.. I doubt if they will find out if I proceed blindly, but I just want to know the legal way of doing things and the fees involved if I chose to do so:P

A condo? Usually for high rise, the separating walls between units can be load bearing, thus it is not hackable at all. You risk undermining the structure of the entire building if you do so. If the wall is indeed load bearing, the upper units can collapse upon your unit since there are nothing holding the concrete slab at the top.
Best people to check with are the management office, but from my 2 previous condos that I have stayed in, none allow such hacking, i was not even allowed to move a door to another wall for an adjacent room.
Good luck

it's possible if there are load bearing beams, and even then, advisable not to break down the entire wall...maybe a third of it

Answer is simple.
Load bearing wall = can not hack
Non load bearing wall = can hack
So, find out which type of wall it is.

Load bearing wall - concrete wall - cannot hack

Non-load bearing wall - brick wall - can hack

You'll be able to know whether it's brick or concrete by removing the plaster layer.

Just try drill some hole randomly check out if is concrete / brick wall. You can feel something different during drilling...... If clay brick then you know what you can see......

Non load bearing wall can be concrete wall as well.
Usually like this
Load bearing wall : Concrete with rebar
Non load bearing wall : Bricks/blocks/Concrete with BRC and etc.

There is one more thing to take note, even there may a brick wall, and can be hack, but most of the time, you may understand if condo not using load bearing wall, which mean they using beam to support, and high rise have bigger beam, so even u hacked the wall, but the beam is very low, is still may feel not hack batter then hack coz of the ceiling height are too low.

Definitely beam is a structural member which can not be hacked.

not recommended. You are not supposed to expose the rebar in any way

+1
Neverever expose rebar for long period.

+1 too.

Furthermore even if you are successful in breaking down part of the wall, what will the future value of both of these condo be when you want to sell it off in the future? Patch back the hole and sell separately is it?

not understand.
Just drill small hole like hanging picture type (dia 6mm, depth 2inch) can expose the rebar???

Ofcause that will not.
The bottom line is, do not expose rebar. If really can not avoid then must treat the exposed bars.

Yes. patch back when situation arise.

hah easier said than done.

Anyway I foresee that you eventually won't be able to break the wall and will settle for using the front door of each of your apartment like you should.

Good luck

Really? just settle for a doorway also no chance? what are my chances from 0 to 100%?

Like some of the others mentioned, it really depends on your building management people. They will eventually have the final say - of course - you can still do it 'secretly' and not mention the doorway as your plans but interior renovation when you fill in the form for permission for your contractor to initiate work.