The trop is included to stress the difference in accent. The first is pronouned with a סגול and מלעיל. The second is with a צירי and מלרע.
2) מג וְלֹא תִטַּמְּאוּ is with a חיריק meaning "do not become טמא," whereas
מד וְלֹא תְטַמְּאוּ is with a שוא meaning "do not make טמא."
Both are definitely correctable. I once heard someone get the vowel right but the accent wrong on #1 (or vice versa, can't remember) and I corrected it on the spot.