In jefferson's time only property owners could vote. Only men, who (arguably) more than women, value liberty more than security could vote. Perhaps Jefferson believed those things could not be changed in a rewrite of the constitution, and that based on that assumption the Bill of Rights (and individual liberty) would not be endangered by a generational rewrite of the constitution. Had such changes happened every generation since 1789 we would not have the world as we see it today.
Therefore, I think taking his comments and applying them to supporting a rewrite after 230 years is not rational or relevant.

While Jefferson said this an other things related to modernizing the Constitution I highly doubt he could anticipate a nation of moochers who would trade their birthright for slave chains and a feed bowl. Sure the Constitution should be amended or even re-written as generations see fit but never should the core of the document be corrupted in such a way as to enslave future generations.

"Every constitution, then, and every law, naturally expires at the end of nineteen years. If it be enforced longer, it is an act of force, and not of right. It may be said, that the succeeding generation exercising, in fact, the power of repeal, this leaves them as free as if the constitution or law had been expressly limited to nineteen years only. In the first place, this objection admits the right, in proposing an equivalent. But the power of repeal is not an equivalent. It might be, indeed, if every form of government were so perfectly contrived, that the will of the majority could always be obtained, fairly and without impediment. But this is true of no form. The people cannot assemble themselves; their representation is unequal and vicious. Various checks are opposed to every legislative proposition. Factions get possession of the public councils, bribery corrupts them, personal interests lead them astray from the general interests of their constituents; and other impediments arise, so as to prove to every practical man, that a law of limited duration is much more manageable than one which needs a repeal." --Thomas Jefferson to James Madison, 1789. ME 7:459, Papers 15:396

well, we clearly know Jefferson said change it up! I think he said every generation which he defined as 20 years. I think the founders saw right away that it was going to be daunting to protect what they had agreed upon. and respect from other nations was built upon might and trade-
I often think about the break up of the Soviet Union or Germany after WWII. One could objectively see the positives for having a Constitution like the US. So why didn't they all adopt it? It's not really a matter of culture. Philosophy matters in the politic. Politics are about pragmatism and power and the philosophy should be the balance check. Most people don't have a personal philosophy. In truth they are mostly amoral. Their views are contradictory and hypocritical-all for pragmatism and expediency. Crowd Theory. ;)