Practising as CA and CS both together....????

No, currently it is not possible. That is why pursuing more than one such course is useless, unless you want to go for job work rather than setting up your own practise. However, I have had conversations with many professionals and they believe that such a provision should be introduced whereby a person can practise on the basis of two degrees atleast since  C.S. and C.A. and C.M.A. have slightly different jobs and are not in anyways conflicting with each other. The logic is that when a person becomes a C.A. and C.M.A.(supposedly) then he will be qualified to do cost audits, so why should any rule stop him from doing cost audits. Currently, a C.A. can do Cost Audit but only in exceptional circumstances and only when Government issues such notification.

I see only one thing against such a provision i.e. a person holding  more than one such degree can effectively take away a larger share of market jobs and creating a job deficiency for one degree holders. Mind you practising C.M.A. and C.S. isn't famous yet due to shortage of work and limited scope. C.A.'s effectively can earn their living by doing very small work which C.S. and C.M.A can't. Also there is an ongoing tussle between ICAI and ICWAI in terms of scope of work that professions from these two institute's could handle. With C.M.A.'s being allowed to be able to perform VAT audits, has made this profession more lucrative than before.

May be in future things will change but I doubt that it will happen soon.....