Can you trek in the low season?

Definitely. You can come slightly earlier or later than the main hiking season but expect lingering snow patches in the early season, and increased chances of rain later in the season. (I’ve hiked in Montenegro in what is generally the wettest month, November, and I can confirm that the potential for getting absolutely soaked is quite high!) Winters in the mountains of the Balkans are bitterly cold with plenty of snow, so you need to come suitably equipped.