How can I run bitcoin-cli with disabled syncing? I have synced about 200.000 blocks and that's enough for my purposes. So I want to use bitcoincli, but when it runs with enabled syncing (by default), my computer works to slow.

How can I disable syncing for some time? Probably I need to set up something in bitcoin.conf, but I don't know what.
You could use the invalidateblock RPC. Bitcoin will not bother checking validity of blocks past that an invalid block.