it's not hard to create a firmware.
But each miner works differently, some a lot more different than others.

The S15/S17 hack ones are simply based on the S9 code with some modifications.
Heck I created the (free) code fixes and firmware updates for the S1, S2, S3 (but stopped doing it after that)

The issue is that those who do create them seem to think that since they spend a small amount of time working on the changes, they should be paid by everyone who uses it, and they can ignore the license requirements when using the cgminer code since they think they deserve to hide their code and break the license - even though the work involved in the free cgminer code they are using is hundreds of times more effort then they ever spent on anything.

No idea why people even put up with this, but I guess a small number of people have no idea what they are doing, and thus pay fees all over the place and don't even realise how much they are losing. Hack fees, pool fees, withdrawal fees, deposit fees, exchange fees, withdrawal fees, bank fees. The first two are the highest of them all for anyone who uses hack firmware.

to be clear the controller looks at the oem psu and reads its name model number.

so if your replacement psu has a different model number the controller says fuck you I want model 1 and you gave me model 1a

I had this happen with whatsminer gear. the psu died they shipped me an upgraded psu

P11 vs p10 and the controller needed new firmware to read the new psu.

It's different for every model or a set of models, for example, the APW9's output is 14.5V-21V DC which is the same voltage for the APW9+, but each is suitable for different models, you can't mix PSUs, the miner won't start.

Also, it's isn't just a matter of matching the voltage, most new miners connect to the hash boards using direct busbars at a very specific orientation, so even if you managed to trick the firmware to accept a different PSU it will be hard to deal with the connectors, so long story short, it will be extremely difficult to use any PSU except the one that the manufacturer itself makes.

This is why one should always stick to buying the same model, doing so, you end up with spare parts to revive different miners, if you have 10 gears, one loses a PSU, another loses hash boards and the 3rd one loses a control board, you can mix the parts and end up with only 1 dead miner as opposed to 3, but if you buy 1-2 of every model, you will be in trouble.

There are other components that fail, but most of the time is a dead chip or a few of them, if you think that is a small problem which can be easily and cheaply fixed then you need to do more research, the average fix for a chip would be in the $100 range including labor, of course it depends on where you live, but if you are going to buy a used gear for $400 today, chances are by the time it needs fixing you can buy it for $200, fixing a single chip for $100 or even $50 does not make any sense, so more often than not and especially with the old gears, once a single chip dies, the whole board is rendered dead as far as logic is concerned.

Another common issue would be the PSU, many gears are known to have fragile PSU, and the problem is, most gears today don't use a universal 12v PSU which you can buy of anywhere, they rather use their own designed built-in PSU which in most cases are hard to find, many people have perfectly working miners that need PSU and can't find them.

..
however if you are a solo miner. making your own block and you had a friend who you want to work on YOURBLOCK well.
you can do any pattern or splitting you like.. and yes you can tell your friend to start at the same sequence as you..
.. but why would you want to.. your doing double work and just wasting each others time..
.

Mikey brings up a good point talking about miners being resold possibly multiple times: You included the point of "free electricity" in the OP. The only reason that should matter is if you are getting used & older, less power efficient, hardware. Point being the question for you that should bring is, "the hardware is x years old, how much longer will it last?"

Are you looking at using/getting old to very old gear?

Why would you even care?
However, to answer:
  Using OEM firmware - no.
  Using 3rd party firmware, because they periodically mine to a special DEV fee pool -- maybe.

Any particular reason you are asking these security-related questions? Are you mining in a country where it is illegal? If you are - BAD idea!

If you are talking about a different miner on the planet mining to a different node/pool that is an entirely different matter. Is it possible they may get the same work at the same time? Sure.

It is also bloody unlikely because the work sent to them is completely random and is defined by the node they get the work from. Not only can/will the work ID's be different but the underlying data itself will be as well because the node/pool picks what Tx's to process and again that results in different work being sent. Also keep in mind that even the fastest hardware cannot sequentially process all possible values before someone, somewhere, finds a block and forces new work to be started. 2³² is a huge, huge number...

Sorry to be bouncing you around the Forum but since you are inquiring about the nuts and bolts of how mining works you might want to move this discussion to the Development & Technical area of the Forum where you will get more eyeballs looking at your questions.

This is again one of those threads, in which I don't understand the most relevant question asked. Why open such messy threads?

Hölpölöpöpööpöööö question jiberrish joo ..

No. As explained before the software feeding work to a miner DOES NOT ALLOW THAT. All miners pointed at the same pool or private node get different work unless you screw with the code on your experimental node. If a pool does it (sends same work) then whoever operates it is a idiot.

As Kano and I have said in 2 other threads you started: NO!
Solo or otherwise the pool software assigns different ID's and therefore work to the miners. If you are talking about their speed - still no because a miner's hashrate varies quite a bit. Even any given single miner will have different hash rates and results each time it gets new work.

If the work generator software is coded badly and doesn't give a different stratum coinbase sig to two different miners, then they will probably mine some of the same results.

If the two miners are exactly the same firmware and hardware, then giving two miners the same work will produce some of the same results.
They will not always produce exactly the same results, since the two miners will not mine at exactly the same hash rate and exactly the same CPU clocks getting exactly the same time between generating internal work.
But typically one would do more work and the other slower one would do a less amount of work that overlaps from the start of the faster miner.

P.S. since you included the term "Pool" in the header. No that wont happen unless the pool doesn't know what they are doing.

If instead your question isn't pool related. and you want to know how mining software that does solo mining, avoids the problem of generating the same work, when you run two solo miners, then you need to ask that in the "Mining Software" section here:
https://bitcointalk.org/index.php?board=42.0