B.Com

As per your request, I would like to inform that CS after M.Com will take 2.5 years - 3 years. You will have to pass Executive level after that you can start your 15 months training. In the mean time prepare for Professional level also and after one year from giving Executive Exam you will be eligible for Professional and thus you can give your Professional exams also. Thus your training and examination will go on simultaneously. Like if you registered in ICSI in Feb 2018 you will be eligible for Executive exam in December 2018, thus you can give your exams and pass your Executive in Feb 2019 and thus from Feb 2019 you can start your training of 15 months which will complete by May /June 2020. In between you are eligible for Professional level exam in December 2019. Result will come in Feb 2020. Thus by June 2020 your papers and training will be completed. But to complete in 2.5 years you have to pass the exams in one attempt.

Yes, it is possible for you to change your college. It is normally possible if your college and the college to you are moving comes under the same university. You can go to another university with the same trade provided your college to accept the transfer.
Your college will lose all those fees that are expected from you in your 4-year studies. So they may/may not ask for compensation. Again you should have a valid reason to get it approved from a university such as change of house, family moving to a new place. Please contact your HOD for this matter, he will lead you to the relevant person. It is not normally appreciated, however you try your luck.