Hi there! To answer your question yes you can! I haven't made many changes to them myself, though I've used medibang for awhile, but the steps are pretty simple.
First you'll go to File > then select Shortcut Settings
From there make the changes you want for each function (all by key press from what I recall) and then you'll save It by clicking Initialize and then OK

I'm not too certain if changes can be made to the cursor but there may be something in the Environment Settings under File
As for any additional issue you might be able to find some useful info on Medibang's Help page
In regards to contacting Medibang all I know to exist on site is this
and as far as any form of a forum would be the Medibang Creators portion of the website