I usually give the phonemic inventory some time to ripe and leave it relatively unchanged thereafter (that is, from a deus-ex-machine perspective; I still let it develop from
Old X to
Modern X, as I do with Southern Wínlandisc and Buonavallese).
Of course, the morphology/syntax does change, even at the same stage of a conlang, and then I don't change the old post just for the sake of updating it – I'll leave it as is (or add the updated version below the original), because then others can see how much work it was to get to the present state of the conlang in question.
And as you may have guessed, piecing together a phonemic inventory for a diachronically derived/evolving language is really a multi-step undertaking.