NOC is a must in order 2 change sponsorship. Companies dont allow for changeover without it. So working without it is considered illegal. Now regarding your query on business visit visa.

These type of visas are valid only for 3 months and are not extendable. However, one can reapply it for another 3 months by exiting country on each renewal. The maximum time of renewal depends on the immigration. I dont think it can be stretched till a period of 2 years.

Find any companies doing PR services and he might answer your query exactly. You can call 5845825 ask him in detail about your situation, may be he can help you His name is AWADD, speaks english well too. Just pretend as you know him through someone.