In the above example, if I wanted to play this clip 10% faster in reverse, the keyframe at the start of the clip would have a Time value of 2324 and the keyframe at the end of the clip would be 1. Manually reversing the clip with a non-preset speed is the same, but you set two keyframes: the one at the start of the clip contains the last frame number and the one at the end of the clip contains the first frame number. To get rid of this, you can right-click with the playhead on the keyframe, Slice -> Keep Left Side. The clip will extend beyond this keyframe, but will just be the last frame frozen until the end of the original duration of the clip. There will be a green tick at the bottom of the clip where this keyframe was set.

2092 frames / 30 fps = 69 sec ( 1min9sec), so I move my playhead to 1min9sec1frame, make sure the clip is selected, and enter 2324 in the Time property. If I want that clip to play 10% faster, it needs to have a duration that is 232.4 frames shorter than 2324 frames, or 2092 frames. If I opened a clip that is 1min17sec14frames long into a 30fps project, so that clip is 2324 frames in duration ( (1min*60+17sec)*30+14). To change the rate to a non-preset value, you need to determine how many frames the clip contains at the current project rate. The same thing works for slowing down the entire clip or reversing the entire clip at these preset rates. To speed up an entire clip using the preset values, you can right-click on the clip within the timeline, select Time -> Fast -> Forward -> 2x (or whatever speed you want).

(Note: My machine which I use for video processing and Openshot development is currently down awaiting a new power supply to arrive, so this is all from memory and may not be entirely correct, but will hopefully get you started down the right path.) Depending on how many of these 'effects' you want to apply to a single clip will determine how many steps it will take to perform each one.

Openshot speed up video