Yes, it is very much safe to visit Kasol as it is in Himachal Pradesh and lies in the centre of the state.
So it won't be any problem visiting the beautiful place.
The border tension does not affect in any manner to Himachal Pradesh.
I have a friend of mine visiting Kasol as i write this answer and from what he says people are very much happy and joyful after what our Armed Forces have achieved today😂 However do keep in mind the route safety as:
1.The roads are very curvy.
2.The roads are single lanes. Thats it, there isn't much to worry about when visiting Kasol.
Do visit as this time will be the best time to visit it.
Enjoy your trip.