Can I add a second disconnect main breaker load panel from the meter trough?
Years ago 3 wire was ok but since the 99 code if memory serves, 4 wire is required, no additional ground rod is required on a connected structure but a separate structure requires an additional ground rod. I have wired quite a few connected and separate buildings including my personal residences since this time.

Removing the meter will protect from back feeding but would not be a normal code compliant method of using a generator
A 10-3 feeder will only provide 30 amps of power no mater what size the sub panel is. 

The best plan is to have a code compliant transfer switch or interlock kit. I know several people that have been back charged for years because of new wiring and a cut seal. They went back to the date on the wire and said the owner modified the meter that was out of calibration. I was only able to help the 1 home owner that I had cut the seal and made a new connection. Back then I had seals but they did not match the electric company’s data so they went back to the date on the wires + 10 years prior, I just replaced the panel with a better quality , permitted, the other 2 had to pay thousands, so don’t think you are getting away with anything and any changes if not permitted and done by a electrician. In the old days I had several sets of seals given to me by the power companies, I put the tag numbers on receipts and permit cards that I did.
I would not want to make a change without making sure my customer is protected, it used to never be questioned, but after having seen several people get thousands of dollars back charges for changes (and I doubt they messed with the meter) were charged because the seal was broken and the date they could prove a change was made. Hope this helps but after seeing this I would be careful and not try and cheat because someone may cheat you in the long run.