Can the ea seller correct the trading signal?

 
I buy EA MT5 for trading, I want to know Can the seller modify the order signal online? or that ea will only work according to the programmed instruction set
 
Either you bought an EA or you subscribed to a signal. Not both. Fix your question.
 
It doesn't have to be something wrong if the sellers signal is different than your EA's performance. There are many factors that determines the trading conditions and even if you have the same broker it can be a bit different result.
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