No, such trivial differences in translation certainly do not affect the validity of the Mass.
While I agree with you, it becomes problematic when there seems to be a history of “magic word syndrome.” If one looks at an old Maronite, there is a very obvious Latinization: the institution narrative goes from being ft. 12 to 90 for the second half (and the recordings one can find have the priest stop and annunciate every single syllable individually). I’m sure there are many that would argue
any word variation affects validity. Each individual word, in this mentality, is necessary for proper form.
I wonder what they would say then if they saw the 80 or some odd different Syriac institution narratives.
In any case, I think “for many,” while a limited translation, is closer in connotation than “for all.” For one it agrees with the general English rendering of Matt. 26 and Mark 14. Secondly, while the Evangelists
could have said “for each man,” “everyone,” etc., they chose not to (I’ve heard grammatical arguments Christ could not have said all in Aramaic - absolutely unfounded). The very fact that not everyone accepts the covenant makes it an exclusive agreement. This doesn’t affect the intent of the priest, nor does it affect the validity, but it does have theological implications.