Is tuning permitted?

No, tuning is not permitted.
Anyone using so-called “tuning kits” or tampering with the Bosch eBike system in some other way risks losing existing guarantee and warranty entitlements on the Bosch eBike system and other bicycle components. In addition, this improper treatment of the system generally reduces its service life. Damage to the drive unit and the wheel may result. Your own safety and that of other road users are also put at risk in the event of possible accidents due to tuning. High personal liability costs and possibly even criminal prosecution may result. Bosch eBike Systems accordingly urges all riders and providers to refrain from tuning eBikes.