Proposed Changes: Following the same guidelines as any other creature capable of such, Striga will be granted the ability to learn Void Magicks save for Fire evocation, Blood Magic, Necromancy, Mysticism limited to the Fourth Tier. They will be able to take two magics up to Tier Four, and two more up to Tier Three.
A striga learning these magics would sacrifice their strength exponentially, as in the stronger they get in the magic, the weaker they get physically, as they peaked their magical abilities they would weaken to the point of only being only slightly physically stronger as a human in their prime and peak physical shape.
Upon learning necromancy, the Striga would no longer need to feed in the normal manner to gain life force, as they would be able to use necromancy to extract it, however both methods would be plausible. However, as a drawback their natural regenerative properties would slow somewhat as a result of the necromantic properties on the soul.
Reasoning: The Striga still contain their soul, and there is nothing in the previous lore that realistically stops them from learning certain magics. According to current lores, if one doesn’t have a soul they aren’t present on the mortal plane we inhabit in a normal manner as other creatures and descendents do. It’s a perfectly feasible thing, as we can see the Frost Witches maintain their physical strength as well as have the ability to cast magic.
Redlines: A striga would not be able to become a Lich/Darkstalker/Ghoul/Wraith or any other creature related to the proposed added magics.
A striga who has taken necromancy as a magic may not heal nearly as quick as they would normally, though it would still be accelerated.
Any striga which uses blood magic must be aware of their RP limitations as Striga, and be aware of the effects of blood on them. Using a small amount likely would not bother a Striga though large blood rituals are an obvious impossibility for them unless extreme measures were taken prior.
Credit to Phil and Tentoa and Yoppl for helping with ideas.