In this three story apartment triplex there is three separate meters and three separate 70A disconnect switch (circuit breakers) and from the disconnect power goes to a panel in each apartment. But the building was never zoned for the three apartments. So what the owner wants to do is eliminate one of the three meters and still use the panels that are in the apartments it will just be one panel per floor. What I want to know is can I move the cable from one disconnect to another and change the 70A breaker to 100A.

Your plan really depends on the total load of both apartments, if 100 amp would be sufficient for both. At least you know you will be limited to 100 amp, if the load is greater then the main will be tripping. Under most conditions, I suppose this would be rare.

If the plan is to connect all three apartments to one 100 amp main, then this situation is exasperated even more.

The other issue is how this would be distributed mechanically. Exactly how would the additional feeder cables be connected to one 100 amp main? You may splice all these cables together with a pigtail to each lug, the enclosure will need to be large enough to contain all the cables and splices.

With the exception of certain perfect conditions, I would not recommend this plan.

Perhaps some photos of the mains, feeder cables, would help to advise you on this.