Is there a shortcut for a synchronized bitcoin core after txindex? I have downloaded the whole blockchain, but I was curious about the working environment after enabling txindex=1 and calling the -reindex command.

Now that I decided not to reindex the blockchain (didn't want to develop anything extreme and to wait that long), I disabled txindex=0 and bitcoind is downloading again all the blockchain!

Is there a shortcut to avoid it? 

*I think the debug.log file is growing twice the initial size
When enabling or disabling txindex the blocks you already have are used, they are not re-downloaded. There is no shortcut, once you start you have to wait for it to finish. The process of re-indexing throws out the state you already have and rebuilds it completely from the block files where possible.