It won’t be a negative if he does well, but now that he’s in 9th grade, it will stay on his CB record.
My D is one year older and had a similar score (650/730) October of 7th, though she was in Geometry. We had her take it again late in 8th so the score would again be discarded by default. (She did well enough, 1550+, that we kept it).
So by the end of Alg2 and 8th honors English, she had enough to cover all content on the test (1 silly mistake cost her a M800). If your son has done well enough on practice tests to be where you want to eventually be, he can take the test now. But because it will stay on his record, evaluate whether additional schooling, practice, etc., would be beneficial and consider taking it later.
NM requires an SAT or ACT between August the prior year (Soph) and December the following year (Sr) to support the PSAT test score. So an SAT score this year would not support NMS qualifying in Junior year to become a finalist - he would need to take the SAT or ACT again.
This puts us in a a similar dilemma - I thought she was done but now needs a supporting score. We may have her take the ACT and not use it for college applications if it is lower.
I would also suggest taking the Math 2 Subject Test this May or June. I know some kids in accelerated math aren’t even aware of Subject Tests at the end of PreCalc, which is the best time to take it.