What if "fake" block in local node

[maplelake]

If we fake block data when "GenerateBlockToAddress" PRC command,such as the nNounce cannot meet POW validation. But we force the block data is written into blk.dat.
The 'error' block data will be broadcast to another node and fails to relay to other node as it is invalidate.

What happen on local node ? Node still receive new blocks and transactions,then validate it.
How to sync blocks because the local node need save it?
How to validate new transactions ?
what is shown in local wallet with fake address ?

[odolvlobo]

Your node will recieve blocks that extend the chain and your "fake block" will be orphaned.

[nc50lc]

^ additionally, your current peers may blacklist your node and you wont be able to reconnect to them for quite a while.

But you said "force in the blk.dat file", IDK if that's possible but if it is, I think your node wont sync past that particular block.
You'll have to delete the related data then reindex to sync properly.

[1] How to sync blocks because the local node need save it?
[2] How to validate new transactions ?
[3] what is shown in local wallet with fake address ?

Hold your horses.... The questions didn't connect at all.
1. It will be done automatically by your node.
2. It will be done automatically by your node.
3. There's no such thing as "fake address" and faking blocks won't affect your wallet.dat.

Based from this questions, you should start with the basics than trying to solve these scenarios.
I'll recommend you to read Mastering Bitcoin, pdf download link in the "see also".
It has everything you need to know.