Your definition of "blasphemy" is wrong, but assuming you mean "against the rules of religion" , I will give you an answer.
By your definition Circumcision & Education both are "Blasphemy"
If "circumcision is blasphemy", wouldn't teaching a child to read and write be blasphemy too?
Humans are born illiterate and they will remain that way if they are not taught to read and write. There are millions of people in Africa, India, China who never learn to read or write, by your definition they are in "natural state".
Allah's order is the rule
In Islam, angels & jinns were ordered by Allah to bow to humans. This in no way means that we humans are superior in any way to Allah, but it simply was "Allah's order".
Similarly, it is Allah's order for us to remove the foreskin. Not removing the foreskin would be "blasphemy".
I would NOT call it "changing Allah's creation", but rather "following Allah's orders"
Priority for Muslims
There are many medical benefits to circumcision, but I can assure you, that for the millions of Muslims those medical benefits are secondary or may be even not of any importance, it is Allah's order that is of prime importance.