He has suggested using the first two weeks to dial in first. Like 10 total sets for 5 reps each, without maxing or max repping.
Then testing for a strong rep max on week 3 and computing that for your TM going forward. After that, he strongly suggests leaving the TM alone and only going by the recommended TM increases (even if you're in the double digits reps-wise on the last set)
So yeah, you should be good to go if you decide to re-test! Though, the 531 program uses a rep max to calculate a TM. Something like a strong 5rm = new tm going forward. Your TM should definitely NOT be your 1 rep max.