add --fee to change fees to other values

freqtrade/optimize/backtesting.py

@@ -63,9 +63,12 @@ class Backtesting:
         self.config['exchange']['uid'] = ''
         self.config['dry_run'] = True
         self.strategylist: List[IStrategy] = []
-
         self.exchange = ExchangeResolver(self.config['exchange']['name'], self.config).exchange
-        self.fee = self.exchange.get_fee()
+
+        if config.get('fee'):
+            self.fee = config['fee']
+        else:
+            self.fee = self.exchange.get_fee()
 
         if self.config.get('runmode') != RunMode.HYPEROPT:
             self.dataprovider = DataProvider(self.config, self.exchange)