Is there any difference between "even if" and "even though"?
If yes, are they always interchangeable in different examples?

E.g: Even (though / if) he didn't like the present, he shouldn't have been so rude. (Which one(s)?)

How about "even though" and "although"? Are they used interchangeably?

Thank you in advance,

There can be some differences in tense and meaning when you use even if or even though. The latter is about a definite situation of which you have some experience. Even if implies a possibility. You don't know exactly what will happen.

I passed this exam even though it was very hard.
I will pass this exam even if it's very hard. (It may or may not be hard)
Thank you Nikoo very much.

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EVEN THOUGH: When you know what is going to happen (it's a fact) for example: You are looking out of the window, and it's raining outside. So:I WILL GO OUT EVEN THOUGH IT'S RAINING. (We are seeing through the window, and it's a fact)EVEN IF: when you don't know what is going to happen, for example: We can't see outside, we don't know if it is raining or not:WILL YOU GO OUT FOR DINNER EVEN IF IT'S RAINING?
Thank you very much Leon.

Another way of saying it is that, as these are normally used, even though concedes that the following proposition is true while even if disclaims knowledge whether the following proposition is or will be true or not. (Still, people do sometimes substitute one for the other if they aren't being especially careful.)

I would say, Even though he didn't like the present, ... because, in my judgment, the speaker was saying that "he" really didn't like the present. (Some would say Even if he didn't ....)

In contrast, Even if he loses his job, he can live on his savings for a while. His losing his job is only a future possibility. We can't claim to know whether he will really lose his job or not. You can't use Even though he loses his job, ....

Although is very much like even though.

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Thanks a lot CJ for the complete reply.