To reverse a 1000 blocks and to catch up then to make the longest block chain takes way more than 50 %, if you want to get it done in a decade.
If you have more than the rest of the network combined (so more than 50% of total power including you), you can grow the alternative chain indefinitely as long as you are ahead. If you have 1% more than the network, you will be 1.44 block ahead per day. If you have 10% more, you will have 14.4 blocks per day. If you have twice the current Bitcoin network, you will reverse 1000 blocks in less than a week.
If you want to do as much of a mess, grow your chain, and wait until the rest of the network caches up with the speed. And then release the alternative chain.