I have a Yamaha RGX 121Z with a Fender-style tremolo, and I would like to adjust its height, to get a more "Floyd Rose" whammy-style, as I´ve seen on this video www.youtube.com/watch?v=mM8-StHlnJw

I am not sure if doing this will increase the probability of going out of tune, or even damaging the tremolo system itself. Can you help me?
There should be a plate in the back, I believe you just loosen the screws nearest to the bridge, and it should loosen it up. I wouldn't mess with it if you care about your guitar. Practice on a cheaper guitar, or find a professional.
If you want a floyd rose whammy style, buy a floyd rose or Edge trem.
Without locking tuning it will just detune. They were built for wobbles.

This guide just allows you to vibrate in both directions.
On playing the Paul Gilbert signature at the guitar store extensively, my missus sighed:
"Put it down now, It's like you love that guitar more than me!"
In Which I replied.
"Well it has got two F-Holes!"