Often i have heard, 'ขอ' pronounced it into 'คอ' ... Is that the case in some part of real life conversation? Take an example, like 'ขอโทษ' , often pronounce into 'คอโทษ'...

I read somewhere that in real life conversation initial syllables are often unstressed, therefore producing a neutral tone.

SimonN is right, and if you're interested in a more detailed explanation you should have a look here:

http://slice-of-thai.com/stress/#citationspeech

(Maybe that's where you read it )

Thanks