Rate wise constraint is no where mentioned in the CCR,2004. Hence, it is allowed to adjust even 5% credit with 12% credit. Yes common CENVAT Credit can be utilized for payment/ adjustment under two different heads, provided that the common input service is not specifically related to any exempted product or exempted service.One need to be acquainted with the Rule 3A of CCR, 2004 where reversal to be made on account of any exempted product or exempted service.

Thanks for the reply........