We have just introduced a new endpoint, which can be used to modify prices (price, common price, purchase price, action price), discount flags and min/max orderable amounts: Update Price List PATCH /api/pricelists/{pricelistId}.
The endpoint is a counterpart of Price List Detail (GET /api/pricelists/{pricelistId}).
Within the request you can modify up to 100 pricelist entries. Provide only the items you want to amend and the others are left untouched.