Are there hotkeys to change the Replayspeed of a replay from x1.0 immediatly to 0 or x0.3 ? I know you can scroll through the speed with , and . but a key which pauses immediatly?

Pauses immediately is P. You can't set it to 0,3 at once though.
You can also use shift+p to enter the next frame if you're paused.
Using E will make you able to edit the replay from the point you pressed E.

Thanks! Is there another Key to make a Jump though not exactly 0.3 but something along those lines?

You can make it 0.3
All you need to do is keep pressing < , until you get there. It's not possible to 'jump' anywhere.

use the > < keys and hold shift to get more precise only works on speeds less than 1 and greater than -1:c

[Ctrl + >] and [ctrl + <] will immediately switch you between 1 and -1, so by using this you'll be able to make your replay play inverted with the same speed.