San_K / app,
What app says is true. If you just put some mettu, it may not be in any known raga or people may not accept it as a raga at all :) I would say people will accept what you put if there is some consistency in it. What it means is certain phrases should be used certain times consistently. Then, not worrying about the raga, you will get a pleasant melody. A lot of music grammar in India has come about post facto. Ragas like 'anadhabhairavi', 'yadhukula kambhoji' etc were part of folk tradition. Later the grammarians tried fitting their grammar. But we must also understand that without a grammar being written down, people were singing Anadhabhairavi consistently. Much of why only 12 notes in an octave and why not more has to do with aesthetics. Any division more than 12 may not be pleasing to the ear. Hence get the slots assigned and then you can so slightly off these slots and give a different feel altogether.