Add a new transaction type of 'Impairment' with its own posting profile and include it in the Fixed Asset Valuation view.

Public sector bodies often have to record an 'impairment' (damage to an asset that reduces its value).

It is a bit like a revaluation but the impairment needs to reduce the asset Net book value and be recorded separately in the GL balance sheet and written off to the P&L as the other side of the journal entry.

Transaction types are not user definable....maybe a few user definable codes code be added with their posting profiles and valuation entries.