Well, it is doable but it wouldn't really be that usefull imho.To add from before I wouldnt mind editing checkpoint times too, but that might be a lot of work for you :\
First, checkpoint times are set by your own run. (Editing those would allow for making maps with unfair/not doable times.)
Bronze,silver and Gold (the goal times) can be manipulated manually. Each checkpoint then calculates a new checkpoint time for its medal, depending on the platin time of the said checkpoint and a scaling difference between the different medal goal times.
Editing the goal checkpoint times of the bronze,silver and gold medal would be a bit cumbersome. (as everytime you scale up/or even change the goal times you have to do that as well with all checkpoints.) It's definitely doable to implement that, but in my opinion it isn't really going to benefit anyone.
Working on that feature right now. It's almost done. Will be included in the next version.I think Ill update it again once theres an update for the time edits.
It definitely isn't easy. (As you need to have a bit of practice/knowledge to pull of some of the tricks reliably or even see how to progress further.)I just had my brother try it, and he hasnt really played much of the game, he got to the 7th CP in like 25 mins, tried for another 5 mins and gave up Lol! So I guess its a hard map..
The fact that your brother was able to pick up the game and get that far is still a remarkable achievement.