Loaded post. :|
It depends what your goals are. If you're talking about being able to instantly transpose a piece in f minor to c# minor, then you can work toward that. It's not impossible.
The more you play in the key, the better you get. Absorbing a piece in a key and then sight-reading a lot of pieces in the same key would help a lot. Knowing the scale, playing the chords in the key, etc., would help too.
The "can a piece in f minor be suited for c# minor?' question is loaded. That's up to individual taste. Some will say yes -- it's just a different key, it's all relationships... Some will say no, that it will only sound right in f minor, the composer meant it to be in the original key, that the original key has the correct character.... So it's not a question that has a definite answer.