Electrical service sizing mix up in Mexico
Why 30A service?

Because of provisioning.  They are not able to provision 50A service at this time at this location.  That is probably due to transformer or pole-line wire capacity in the neighborhood.  Giving everyone 50/60A service means they would be oversubscribing their transformers and pole lines.  This would necessitate a big capital expense upgrading those, and that is not commercially feasible right now.  

If you want more service, tell them you need more service and pay whatever additional they charge you for the additional "share" of the transformer.

Safety regs

Given that you think inspection does not exist, can you just ignore safety regs altogether and do what you want?  Sure, what could possibly go wrong?  


If the power company charges extra for fitting a 50/60A breaker, and you haven't paid the upcharge, then if you fit a 60A breaker behind their back, that is plain theft of service.  I don't know how that's handled in Mexico, but it would be well within their right to remove their service drop and refuse to provision to your address any power at all. 
If the transformer blows up, they are going to quickly walk the street and see which neighbors have illegally changed their 30A breaker to 50/60A.  They will be deemed responsible for the transformer blow, and they will buy the neighborhood a new transformer and wiring.  
If there is a house fire in any way relating to this, the fire insurance will balk at paying, and because an illegal act was behind it, the mortgage lender will come after you personally for the value of the house. 
It may be a challenge to sell this house in the future. 


Getting 100A out of 2x50A

Split-phase power doesn't work that way.  

If you had 50A@240V service, which you do not, you do not have any way to get 100A@120V.  What you could get is 50A @ 120V in two instances.  

So if you have a single 100A@120V load (not likely) you could not power it off 240V/50A service. However, if you have eight 12A@120V loads, you could put four on one side of the service (48A) and four on the other side (48A) and you'd be solid.  Derating notwithstanding, of course. 

Electric large appliances out of this 30A service

Not gonna happen.  


If you attempt to run an 30A electric dryer, it would have to be the only large appliance running at the time. 
A 30A electric water heater is impracticable because you can't control when it cycles. 
An electric range is Right Out; they draw too much. 
A 240V/30A air conditioner is also out of the question, since it runs too often for "turning everything else off" to ever work.  


If you have any of these coming in, talk to the power company, or Craigslist.

If you have a 20A-breakered (16A) 240V appliance, that might have a shot of working.