That essentially is the problem with all mobile solutions including the MBP's. The cooling for mobile units are designed at the edge of thermal dissipation requirements to maintain the form factor but also provide enough cooling to operate the laptop at load periodically. However rendering especially with applications such as Premiere or AE can take hours and the cooling efficiency is not designed to handle that heat generation. Mobile cpu's like all Intel CPU's now days will throttle down to far lower speeds and power draw to give the CPU time to cool down to prevent thermal damage to the CPU's. That temp to start throttling is normally 90C. The higher above 90C it goes the greater the CPu throttles. This prevents thermal burn on the CPU most of the time but long renders that take greater 2 or 3 hours constantly will eventually cause thermal damage to the CPU anyway just from operating in the 90+ temp ranges at such long intervals so often. Also the efficiency of the cooling in the laptops drop over time from dust and fan wearing which can accelerate the time it takes to start thermal burning a chip. The short answer to your question is yes you can do this at times but the MPB is not designed to handle this thermal load long term on a daily basis for long periods of time. I suggest you start looking at a desktop solution atleast for the rendering aspect if you must render often and the laptop is the only system you have right now.
my Asus G750 ROG laptop has no heating issues due to beefy cooling system which provides separate fans and copper cooling for the CPU and GPU.
The Appl products seem to be falling further and further beh&ind the beefy Windows gaming laptops....maybe time for a change.