Yes, you can, however, the 65W (MacBook) charger will charge the battery much more slowly, and under some conditions might overheat if you're using the computer and attempting to charge.
In a pinch you could do it, but I wouldn't suggest doing it long term. On the other hand, if you're going 85W to a Macbook, no problem.
I would expect that they have some sort of internal thermal limiter, but that's no guarantee that it wouldn't overheat.
MacDann