You'll need to make an item or chat command that triggers a script that turns you into a werewolf or the wolf form.
The script that turns you into a werewolf or a wolf will use mainly a polymorph command that looks like this.
eVis = EffectVisualEffect(VFX_COM_CHUNK_BONE_MEDIUM);
eMorph = EffectPolymorph(iMorph);
//Make it an Extraordinary Effect and thus not removable via standard dispel.
eXMorph = ExtraordinaryEffect(eMorph);
ApplyEffectToObject(DURATION_TYPE_INSTANT, eVis, oPC);
ApplyEffectToObject(DURATION_TYPE_PERMANENT, eXMorph, oPC);
oPC is an object pointing to the PC that is shifting.
iMorph is an integer refering to a line in the text file polymorph.2da.
You will have to place an edited version of polymorph.2da in your NWN\override directory. You can find the original in the NWN\source directory. Add the new shapes for your custom werewolf in polymorph.2da after the default ones already in the file. You can change a few things there like portrait, appearance, claws, bite and skin, bonus hitpoints and bonus to stats.
Once all of this is done, you can also additional bonus by adding item properties on a skin that is equiped when you shift into a werewolf.
I hope that helps a bit to get started.