I'd advise against tweaking the types of were creatures for the simple fact that it doesn't fit the feel of the intended use of the wolves as a plot device. They are Strahd's werewolves. One thing you could consider is to turn it not into as much of a combat encounter, but a roleplaying/morale delima. My players, for example encountered the wolf pack around the same level. I had the bulk of the wolves out hunting and prowling the woods looking for the party (who snuck by them due to having a ranger with pass without trace up), with the female werewolves looking after the elders and children. They ambushed two of the she - wolves and ended up being told to speak with the named werewolf (can't remember her name at present, but she's the mate of the werewolf currently in the castle dungeons for causing a scism. Basically I played up Kiril as being this sexist thug of a jerk who was quite literally making the women stay in the cave and guard her under the supervision of his mate (I think her name is listed in the book, she has blonde hair). The pack basically only follows Kiril (and Strahd) because they fear him as Strahd's chosen, and would likely betray him if given a chance. They may not willing side against strahd as long as their other leader is in the dungeons, but I had their pack offer to "have trouble finding them" if they managed to kill Kiril. She also suggested they take the children in the cave and use them to lure Kiril's hunting parry away so the ones in the cave wouldn't be forced to help fight the party. My group ended up taking the encounter to Rictavio's Tower.
...whether any of this helps you is up to you.
For combat options, I'd suggest looking into the cave mentions about the "Blessing of Mother Night". It doesn't outright give a mechanical boon, but gives a good concept of how to potentially buff the werewolves. I'd buff Kiril if nothing else, and maybe give the wolves more health. I for example gave Kiril extra health, and made his damage immunity be resistance even to magical weapons. I also made his attacks do extra necrotic damage, and gave him legendary actions to give him extra attacks and a shadow jumping ability like the shadow monk. It sure suprised the hell out of my players when he appeared magically in the tower window the cleric was taking sacred flame potshots out of from the top of the tower, and he had a hell of a grudge against the party rogue, who shot out his eye at the start of the campaign. ☺
