I asked some professors for recommendation letters for my MEng in Mechanical Engineering after having completed my BEng in Mechanical Engineering. I am looking to apply for an MEng in Computer Engineering at the same university. I do not have work experience in computer engineering so could I ask the same professors to ask for recommendations, since no one else other than my mechanical engineering professors is in a better position to write a recommendation letter? If they write a very similar or the same letter would it affect the chances of admission, if the admission committee realizes they are the same or from the same professors?
In the US it would be completely normal for letters to different programs to come from the same professors. Admissions committees here are looking for general indicators of success. An exact match between the letter writer and the program isn't needed or expected since it is common to switch fields after a bachelors.
While the fact that the letters come from the same people might be noticed, it wouldn't be remarkable. And, it is possible that there are different committees in any case.
In most cases identical letters wouldn't be an issue unless the letter is too tailored to one specific field.
But you could talk to the professor(s) about how they feel about their recommendation for a somewhat different field. They may have some advice for you.
I'm not sure that this advice/answer holds outside the US, however. The preceding paragraph here probably works most places. Have a conversation. "Are you comfortable also recommending me for computer engineering?"