@Wokkeltje: the second and third you mentioned:
* For temp: be able to modify the +-4%
* For Precep: be able to modify the +-2%
are already possible in the latest firmware. Specifically, you can change the weight of each factor. For example, by using a 50% weight for the temperature factor, it essentially changes +/-4% to +/- 2%.
The first one you mentioned: changing the threshold of 30% is currently not possible.
Note that if the algorithm doesn’t fit your need, you can always host the weather script on a different server and that way you can modify the weather algorithm in any way you want.