Quote from: Severos on January 20, 2018, 03:58:46 PM

Is such attack possible in theory?

No.

Quote from: Severos on January 20, 2018, 03:58:46 PM

if not, then why?

There are 2 reasons.

The most important reason is that the consensus rule does NOT state to follow the chain with the most blocks. That is just an oversimplification that people use when talking about the blockchain because it works in the general case and it is easy to say and understand. The ACTUAL consensus rule is to follow the chain that has the largest total proof-of-work. Since your blocks will be solved at a lower difficulty level, the total proof-of-work will be less than the "real" chain even though your chain has more blocks.

The secondary reason is that Bitcoin Core (and any other node or mining software that is 100% compatible with Core) has checkpoint hash values that it compares against the blockchain. Any chain that doesn't match those checkpoints is discarded.

Quote from: Severos on January 20, 2018, 03:58:46 PM

if so, what effects would it bring to BTC? and how would we prevent it??

It brings no effects since it isn't possible. We prevent it as described.

Quote from: Severos on January 20, 2018, 03:58:46 PM

I've originally wanted to test this idea in a local setup before bringing it to public, but I don't have enough technical knowledge to implement it.

You've saved yourself a lot of wasted time and effort.