Can you use a Perdo Mentem effect (Quell an emotion in a person: Base 5) in order to remove the pain from injuries and thus the wound penalties ? The wound will still be there, but you can act without the negative modifiers.
As I understand, pain isn't an emotion, so much as a sensation (lit: something you sense).
To get rid of Wound penalties, have a look at ArM5, p. 134, ReCo guidelines, base 10.
While the traditional approach is via Corpus, it is definitely possible to use Mentem. The relevant conversation is "The Hermetic Art of Mentem" in Art & Academy. According to the Muto Mentem guidelines, pain is governed by the common sense. (p.33). A Perdo effect would destroy the pain for as long as the spell lasted. A Rego effect would allow you to control the common sense and make it feel something else other than pain, in a single-minded fashion. Muto could turn the pain into another sense, such as sight, smell, or hearing, probably with differing negative game mechanics such as blindness, nausea, or deafness.
To a point, yes.
Ultimately, a Wound Penalty is the result of both pain and actual physical damage to the body. The "Medicine" chapter of Art & Acadame provides a chart describing what sorts of injuries are equivalent for each wound level beyong Light: Medium Wounds are equal to a broken hand, a pierced kidney, maimed foot etc and it only gets worse from there. As such, it may be questionable just how much good an analgesic will do.
That being said, the Theriacs in the same book do indeed allow a character to create soporifics which reduce Wound Penalties by causing patient to gain Fatigue. It's Non-Hermetic, but might be used as a boilerplate. Likewise, there are a number of pain-removing spells that use the Creo Corpus guidelines, any one of which could form the mechanical basis of your proposed spell.
By my calculations, the spell ought to be: Base 5, +1 Touch, +2 Sun = 20.
Thank you guys, you are really helpful and I really love this forum because its members are so helpful.
But gush, I really need to buy more books! 
“A man can never have too much red wine, too many books, or too much ammunition”
― Rudyard Kipling
I actually GM'd a Broken Covenant adventure back in 2nd ed where a Criamon PC wanted to cast spells on the grogs such that they wouldn't feel pain or fatigue so that they could carry the bell without delay. Ended up killing a very popular grog because ignoring the signals of your body's limits is never a good thing.
I remember getting my lip numbed up at the dentist. Just from accidentally biting it and not noticing it was all swollen within a couple hours. Even a touch of blood. Erasing the ability to feel pain leaves you in serious hurt really quickly.
I think that not feeling pain would help, especially for activities that don't use the wounded body part, but... it could easily lead to worsening the wound. In fact, you should probably require a recovery roll to see if it gets worse whenever you do and apply some sort of penalty.
Isn't this basically leprosy? If the grogs know a little about the illness, they would have another cause to distrust the Magi.
It's a symptom of leprosy, certainly.
Thanks for reminding me 